The only automatic available with the 54 truck was the Hydramatic, but the cast iron powerglides were available in the Chevy sedans, Bel Airs. You need to know if your powerglide originally mated to a 6 cyl or the 265. If it was from a 6 cyl engine I believe that there was an adapter ring to mate to the older stovebolt pattern, otherwise it would have the standard later GM trans bolt pattern.
Although I personally feel that a newer 700R4 or even TH350 would be a better trans choice if you are going to the trouble to source a new flexplate, starter, driveshaft and rear end. (I realize that the powerglide is a fresh rebuild but TH350's are inexpensive and easy to find).
Mr. Langdon has the adapter for the newer trans if you are interested:
http://www.stovebolt.com/techtips/trannyswap.htm