I don't have the specs with me, but I don't believe the 54 frames are the same. One significant change that occurred in '54 was the increase in the bed size. When my '54 is next to an older AD, the difference is pretty noticeable. This is not to say it can't be done, but it's likely it won't be a bolt-on application.
I believe another bolter maintains this site about GMCs - you may find technical specs to help here:
http://www.oldgmctrucks.com/page0024.html
