What are my options for bolting a different trans up to a slant 6 bellhousing?

There are 3 different slant 6 bellhousings that I know of from '70 up: 3 speed, 3/4 speed floor shift, and 3 speed OD. They all have different size collars with the OD being the largest. I have bolted all 3 to various slant 6's but all '70 and up engines. PS: I have a spare '74 3 speed column shift tranny for sale: make offer.
Later,
Bruce B.