[Brad54]

Some answers to questions:
Speedo gear: same as the Th350. This is a two-part gear: the one that goes on the end of the speedo cable, and the one that is "attached" to the output of the trans. You pull the speedo cable "port," and replace that gear. They're colored for reference. You shouldn't have to change the gear that's part of the output of the trans--so you won't have to pull the tail shaft housing.
Mounting patterns, aluminum and iron case:
The aluminum case has two different mounting patterns; one is like the standard Muncie pattern and bolts up to our stock bellhousings. The other has one side squared off like a Mopar, and requires the factory re-tooled aluminum bellhousing.
That bellhkusingndoesnt have side mounts--it's like a later Chevy bellhousing, but with the funky mount.
There are two different aluminum bellhousings:
One with regular mechanical linkage, one with a boss for a hydraulic slave cylinder to push the clutch fork.
Input shaft lengths and diameters are all standard GM, so the original throw out bearing and clutch disc works.