The converter also protrudes from the face of the bellhousing about an inch or so when fully seated vs the 1/2" the converter is recessed into the face of the bellhousing on gas versions and non lockup diesel versions. It's not because the bell is cut back, it's because the converter is thicker to accommodate larger, heavier duty components.
You could cut the bell off a 46 or 47 and use an Ultra Bell for a 727 to B/RB pattern or an adapter for the 46 gas engine trans but you are still stuck with the smaller and narrower converter.