Thought I'd leave an update on the busted Sigma. I since found out this busted sigma was somewhat considered a write off. The top was broken along both sides of the neck block and considered a fatal break aside from replacing the top.
Not to be swayed and what to hell..."nothing ventured nothing gained" so away I went with my wife's steam iron in my hand and a piece of clean rag. Since the back had become unglued at the neck block, I decided to remove the back to better see the "fatal wound".
After applying lots of heat,( lesson #1...don't get your iron too hot!It discolors the laquer.)I was able to get the back off with no damage to the kerfing. Applying water to the inside seam with a syringe helped considerably. Sure enough, the lower side of the top was broken right through and the upper side of the neck block was broken as well. To compound things, one of the cracks extended right under the neck block and was inaccessable without removing the neck/fingerboard.
Gently pulling the neck of the guitar in a lateral motion, I was able to get the broken top back into it's original position and set it with a couple small dabs of superglue. The upper brace had also broken away from the top.
After several hours of pondering the problem ( I have too much time on my hands), I finally decided that the only way to regain integrity was to "extend" the portion of neck block to include more top area. My reasoning was that 99% of the guitars sound comes from the larger body area near the bridge, I may be able to distribute some of the neck pressure across a larger area of the top with minimum ill effects to the sound. A strip of spruce top reinforcement had to be shortened to accomodate the "wings" I was about to add to the neck block. The "wings were made out of a piece of pine similar to doorstop material. It was sanded into 2 pieces about 3/8 " thick, 3/4"wide and approx 2.5 " long. these were glued to the neck block and the top at the same time with the 3/4 inch side on the inside of the top. Next I had to secure the main brace to the top again. To give it some added strength, I cut two small triangular pieces to repair the cracks extending down to the sound hole. These were made from a piece of eastern white cedar which was split down to approx 1/16" thickness, then sanded smooth then glued cross-grained to the underside of the top once again. Two pieces were used to ensure access to the truss rod adjustment but 1 piece could have worked as well.
Satisfied I had done all I could to keep the neck from moving, I turned my attention to the rest of the guitar. I was right about it being bulletproof. As a side note, this sigma had a mahogany plywood back and sides and was not given the designate DR-18. I still think the Dr-18,28,35,& I can't remember a 41 or 42 all had the solid back and sides as well as solid top.
Anyhow I digress....the glue job was sloppy with drips left all over the place, the gause support at the cross brace junction was extremely large and extended down on to the bridge plate. The bracing was pretty much standard martin braces and don't spare the glue. A support was placed down the center of the top like a running cleat to avoid the top from ever splitting or cracking. The bridgeplate was made from rosewood plywood once again dripping with glue when it was applied originally. This will never do so I took my trusty knife and proceded to cut away any cheesecloth support that was in contact with the top or bridgeplate and cleaned any large drips of glue that was visible. Then with a dremel tool I proceeded to scallop the braces into something like a cross between the old pre-war martins and thier more modern design.I took out a considerable amount of wood all the while wondering am I doing the right thing. I had some examples of pre-war martins and current bracing patterns but I had to adapt the slightly different brace style in my scallops to fit the newer style of brace. Satisfied that I had taken all I dared to out of the braces, I turned my attention to the bridge plate. Well, fools walk where wise men fear to tread and I was jogging pretty good so out came the dremel again with the sanding drum and on to the bridge plate. I didn't think it should be glued to the X braces as well as the top so the whole bridge plate got a bevel job except for the strip where the strings poke through. I left a piece untouched about 1.5"wide along the whole length of the bridge plate directly under where the bridge glues on. Whoops....the grinder hit the center support cleat that run the whole length of the top. And then it hit it again. I own a guitar made by luthier Marc Beneteau and it don't have those cleats so off they come.A little hand sanding along the braces to skinny them a little more and it's time to replace the back before I go too far...if I havn't already. Ok...back is glued on but I still am not satisfied with the resonance to guitar makes when the top is lightly tapped with my fingers around the bridge. Time to get rid of that glossy plastic finish. I get my sanding block and see it has a used piece of #80 grit sandpaper in it. Now it took a real act of courage to take a perfectly good looking guitar and run a piece of sandpaper across it. I closed my eyes and decided to scuff the top once so I couldn't chicken out. As the sanding block hit the top of the guitar, it was very much like hitting a piece of window glass. I opened my eyes and looked in amazement at the tiny little scratch this sandpaper left on the guitar face. With a renewed vigor I attacked the top once again only this time with my eyes open. It was like trying to sand lexan or plexiglass. About an hour later and a couple sheets of sandpaper I managed to take off about 2 cups of plastic off the front of the guitar. Tapping the top once again, success, the guitar was starting to sound like a drum and not a block of wood. With a renewed enthusiam but still guarded that this thing was not going to fold up after I put the strings on it, I went at the back of the guitar. I think I got about 2 cups of shavings off it as well. A small increase in the resonance was noticed but not near as dramatic as when the top was done.
Off to town I go to get new strings and hope this thing works out. After all, I've put quite a few hours cutting, sanding, glueing etc.
By my calculations, the strings are going to be way too high to play comfortably and the slot in the bridge don't appear to be deep enough for me although I don't have a spec to how close the saddle should be to the actual guitar top itself. This one looks like the slot is cut too shallow in the bridge. Oh well I can't wait I'll shave the bone down to get the correct height and maybe after
i get a spec someplace I'll modify as needed. The neck releif looks pretty good so time to string it up and see how it sounds.

I am happy to report that the guitar does not go out of tune, is still holding (3 days now)and I am tickled pink with the tonal response and volume. Not very much bass ( I'm used to rosewood bodys)but very well balanced all the way up to the 14 fret. It is very much like playing a new guitar and over the last 3 days the tone has improved noticeably as well. I'm sure it would fool the most passionate D-18 fan into thinking it was the "real thing".
Anyhow...I don't know how long this stripped down "hotrod" will hold together but I'm sure enjoying it until then.
No Guts ...No Glory.
Thanks all...I'll post again sometime to give you an update.