There are at least 6 bellhousings that fit a 216/235/261 and GMC 6 that I can think of. There are car and truck bellhousings and each one fits a certain era of production. Some have provisions for the pedals to mount, some have provisions for a hydraulic clutch, some are for the early square mounts and some for the later angled mounts.
The car bellhousings don't fit SM420's because the center hole is differant (too small). The crashbox (4 speed lockout) art deco bellhousings don't fit the SM420 either, but a genuine 1949-53 truck bellhousing out of either a GMC or a Chevy will fit an SM420.
He's not going to like the reverse lockout 4 speed, it is a constant mesh box without synchronisers.
