Going back to the Wookiepedia article, and something I believe written on one of Decipher's SWCCG Y-Wing cards, the Y-Wings from Ep. IV were basically the Republic Y-Wing with most of the panels removed. I believe Decipher added the reason: they had so many mechanical problems the Rebel maintenance crews just left the panels off to shorten repair times.
Wookiepedia says:
When Joe Johnston refined the Colin Cantwell and Ralph McQuarrie Rebel Alliance Y-wing designs for construction into a visual effects model for Star Wars Episode IV: A New Hope, he posited that the starship was once a sleek vessel that was chopped and stripped like a hot rod by Rebel Alliance technicians. The BTL-B is apparently the stock version of the "stripped-down" Rebel ships.
So the Republic Y-Wing should have the same lines and size as the later Y-Wing. The biggest thing I'm seeing, as far as accuracy goes, is the nacelles being raised a bit from where they should be. But its a pretty good start, and it looks fun to play with. Nice job.
