Should I make the swap to G3?

Glad you're talented enough to build your own harness!

The guy is pretty talented, you should read his build thread. I think the harness would be the easy part for him.

So just mounts, oil pan, headers, trans adapter or flywheel.

Shouldn't need a trans adapter, bolt pattern is the same outside of one bolt the G3 doesn't use. Definitely will need a flywheel, though.