Originally Posted by jimfulco
Another potential difference in bellhousings is the size of the hole where the transmission front bearing retainer rides. I don't remember the exact dimensions, but there is a small difference which can cause misalignment if the hole is too big.
As far as I'm aware, there are only 2 sizes of front retainers. The 'car' retainer is smaller, and more popular. It is also the same size as the retainers used on the old SM318 3-speeds, in cars or pickups.