Three sheds,

This is not a difficult process on a Lowden ( or to a degree on many other guitars ), regardless of what some may claim to understand of the process.

Firsty your Lowden should already have a predrilled tail pin hole, ready to take the standard endpin jack preamp. The biggest fiddle here ( after everything is soldered to the right connections on the PCB in the endpin jack ) is making sure that everything is screwed in nice and tight ( outer and inner hex nuts and the outer screw on socket cover.

Secondly, your Lowden is predrilled with a hole in the base of each saddle slot to drop the cable through from the split pickup you will
need for your Lowden ( these are readily available as a variation on the standard Fishman matrix 1 and 2 set ups ).

Thirdly, you do not have to route out the slots for each pick up. Lowdens are supplied with a hard wood shim under each saddle, which, ingeniously, is the same thickness as the average Fishman under saddle pick up. This means that tyou simply remove the shims and replace with the pick elements.

Once the wires are dropped through the predrilled bridge plate holes, you can follow the supplied instructions and solder in the connections to the appropriate point on the PCB in the endpin jack.( This is definitley the most fiddly bit to handle.

The other key job is to fit the battery holder to the neck block. Rather than drill straight into the neck block, it is better to screw the battery holder to a very small block of wood ,just deep enough to take the very short screws and then glue this to the end block. This can then be removed at later date, without further affecting the internal look of your guitar.

After this you will need to fix up the cables running around inside the guitar with the supplied cable retainers that will fix to the inside rim of the guitar.

There are, potentially, issues of string balance to watch out for if the base of the saddle is not absolutey flat, or if the saddle is filed down so low that the string does not exert enough downward pressure on the saddle due to break angle. The former means ensuring that the base of the saddle is refiled flat, however, my experience of Lowdens is that you should not have a problem with this using the factory supplied saddles.

Hope this helps