I guess when you say the hub, you really mean the pilot of the converter. The hub goes into the transmission and the pilot goes into the crankshaft. If it is the pilot you're talking about, no you can't use the smaller diameter hub in the larger pilot hole in the crank. Some will tell you there is a bushing that you can install in the crank to enable you to use the smaller pilot. I guess it works, but IMHO, kind of a mickey mouse fix. From the limited information you've supplied my guess is you've got an early (Late 1962 to 1967) Converter with the small pilot. You haven't said what year the transmission is. The 27 spline input shaft didn't come into play until 1968.