I'm confused about the compatibility of a pre/post 67 slant transmissions, with a 66 225. The slant that I'm building is a 66 block with a 66 crank so I would need to use a 66 or older tranny right? What is the reason for this?

I think you can use the '67 transmission-it's the '68 and newer cranks that had a bigger pilot hole in them for the torque converter hub or pilot bearing.

You can use the early small pilot crank with a late trans if you get a converter made with a small snout on it.
http://www.slantsix.org/articles/hrm-sl ... ov-pg2.jpg

_________________
Official Cookie and Mater Tormentor.