Yeah....having a great platform to start with , but i dont know what i want !!

What would I do if it were mine:...
I know you said you're fed up with the 360 in an A body recipe but there's a good reason that happens so often.

So what I would do is go with a 318 or 360, get it running and work all the bugs out. Then get the car nice with all rust repaired and new paint everywhere.

Then I'd drive the car and get to know it well. Then I would look into swap options out there.

Its hard enough to get stuff working together that was meant to work together, even tougher to fab and get stuff working together that was never meant. Plus it's easier to modify a car that is already alive, at least that's been my experience.