I think the only diffrence is the backing plate, drum and associated parts.. I just looked in my chevs of the 40s catalog, and '51-'60 is the same P/N for the brake drum. '49-'50 is not listed.. '51-60 uses 4 of the same drum, which would need to accomodate a 2" shoe, the rears are 1 3/4" same as '49-'50 all the way round, so '51-'60 drums should work on the old backing plates if you need drums and can't find a donor car