Crank register/T converter snout ?

Someone told me that I may need a crankshaft adapter to use my current T converter. The swap I my do is from my current 1966 273...to a 1985 318. He said that the crankshaft register my be different, and the there were adapters to solve this problem. Can someome give me some information about this? and were to get this adapter if I do this swap. Thanks Guys.