You have a double bearing housing . Single bearing housing was used quite a bit later. Looks like a 270 drive to me.

Fun useful fact -

The mounting ring (37) has a few holes that are tapped the same thread as the mounting bolts (40). I think it's 3 but not sure.

Put grease or antisieze on a few of the bolts and put them in those holes then run the bolts in to pull the ring off. It can be difficult to remove.

Someplace in my archives I have a couple of alignment tools that one of the race guys made up to get the engine mounted in the right place. I'll try and post some pix later.