interchange

There is no PCV valve compatibility issue; feel free to use whatever valve cover you want ('66-up covers are easier to find valves to fit).

Unless you happen into a pre-'67 motor, the oil pan and pickup and carburetor would want to be swapped from the '61 engine onto whatever engine you wind up using. The '61 engine mounts would need to be used. Manifolds can be early or late, doesn't matter. I'm pretty sure Charrlie_S (user name over on slantsix.org) has the adapter ring needed to use a '68-up Slant-6 engine in front of a '67-down automatic transmission. If your original engine is a 170 and you install a 225 or a 198, you'll need to space down the exhaust headpipe (flange-and-gasket sandwich) otherwise the headpipe will hit the floor.

Check if the Lancer you're working on has an aluminum block 225. If so, you'll want to hang onto it.