The little 170 cuber. Quite a nice car to meander in. Underpowered, but a six seater with a nice 115 inch wheel base is a good size today. And people look.
Stock engine was the smooth, quiet four bearing Pursuit 170, with a manual 3 on the tree column shift, without syncro on first, IIRC, then 221V8, optional 260. I think the 200 was a 64.5 thing, and it wasn't untill later that the seven bearing 200's cam out.
Plenty of scope for improvement. A later seven bearing 200 'may' go in if it doesn't have a big bell housing, but I'm not sure what happens if its a two-stage or C4. And the manual isn't the same as the later all-syncro boxes.
Best you talk to Al. He's got the monoply on great info for these forgotten Fords.