I have just acquired a copy so can report. First, Pied Piper, your query on 3/2 tunes. Yes, there are a few. None distictively Welsh that I have spotted. The familiar Cheshire Rounds and Shropshire Rounds are in it, also a RoaringHornpipe( compare teh title Rolling Hornpipe found in many English collections). Thse three apparently noted by John Thomas himself. Also the Foxhunters Hornpipe (the tune found in Ireland in 9/8 as Foxhunters Jig). John Thomas's 3/2 version would appear to have come from a published London source(that is editor Cass Meurig's opinion.She assumes John Thomas had access to such books. Quite possibly, but equally well he may have used fellow fiddlers notebooks, as is commonly the case. In either case, it surely came from the published source originally, the details are too consistent for chance).
Ravenscroft's Hornpipe also appears(again copied from a London book, according to meurig).There is a Collier's Round(notated in 3/4), which is also a 3/2 hornpipe(no published source identiied by the editor). The Dusty Miller is also here(in 3/4).
    Well there's a selection, Pied Piper. cant say it's exhaustive. Strongly suggest you get a copy yourself.
      This is a totally splendid publication, recommended reading for anyone interested in British fiddle music. I say british rather than Welsh, following Cass Meurig's general thesis that John thomas was a working fiddler, and had the general repertoire you would expect from c 1750: all the hits from England, Scotland and Ireland, plus a good smattering of locally originated tunes. The Welsh nationalist revival came later at the end of the 18th century, which tried to purge Welsh collectiosn of alien English material(or alternatively, retitled it into Welsh). The Welsh language material is of greater interest to me, as I am more familiar with the mainstream English stuff, but to seee the whole collection is a wonderful education. It is of much more interest as a whole, to take out and isolate the "Welsh" material would seriously distort the picture.
   It is by far the most detailed account of a fiddler's MS book I have seen, the notes and the tunes are wonderfully detailed, and the fruits of obviously backbreaking detailed research. A must have book. I wish there was a Ph D student working on every fiddler's MS book producing stuff like this, we'ld all know a lot more. Well done Cass Meurig.