The Concertina.net Tune-o-tron is a faulty converter. I strongly recommend switching over to the folkinfo.org ABC Converter--which is much fuller-featured and also produces much better scores. With the latter converter, there are no note irregularities--and unlike the Tune-o-tron, it won't munge chords like simple dominant 7ths!

For chords, this is what I come up with:

|: G . D . | C D7 G . | G . C G | Am D7* G . :| see [1]
G Em D . | Em A D . | D . G . | A (A7) D* . | see [2]
D Bm Em C | Em A7 D . | G Em Em/B C | D7 . G . |]

[1] or D9 / Am+4
[2] or C/D D; in the first chord, the dissonant note is a suspended 4th.

I've been trying to work this into the ABC, but first I have to find out if I can used a "decorations" line to put chords where there are no notes (like on the beat between a dotted note pair) and how I can alter the strum pattern to solid chords, instead of alternating bass and chord. In a pinch, I could write an explicit guitar part, but not today.