What will fit / work?

You are right about that...I should of been a little more specific about my question. I've mainly dealt with 273's and 318s...There are quite a lot of LA engines here to be had locally. My main concern was encountering problems (mount location etc.) in the application of the "newer engines" (80s and 90s) in a 65 chassis.
Norm
Hey Norm! Again, Any LA will swap right over with zero fitment issues. The only issues would be;

The use of a Magnum engine and “The Truck Oil Pan.” So dump the truck oil pan for a passenger car pan.

Engine mounts for the 340 & 360 are slightly different on the drivers side only.

The 360 is externally balanced and that is solved with a B&M flexplate. Then you can use any neutral balanced converter which is cheaper.

Thats it! Enjoy!