I love the 54 and 55 1st series, they are much better looking than the ealier models. My unmolested 54 means that there is over 50 years of rust, leaving it needing one of everything.
I don't know of anyone that rebuilds the powerglides, but
www.charlietranny.com and cobratransmission.com have rebuid kits for the early 'glides. Reid Racing and Transmissioncenter.net have Hi Performance parts for the later model glide, they may be able to point you in the right direction. I've purchached parts from Transission Center for a 700R4 and they were good quality. The technicians were very helpful too.
I believe most guys on this site are going to tell you that the early powerglide is a good boat anchor, especially behind the 235. I don't have any experience with it so I won't tell you either way.
Good luck!
