318/360 production info
My vote is 318, any year prior to Magnum.....my reasons are:
Motor mounts direct swap
In keeping with bone stock/dependability, exhaust manifolds......a 360 might get chocked up a bit
No external balance factors to worry about
Swap the 273 damper, front cover, water pump over, no radiator change, no "where's my timing mark"
You are looking for a driver, not a hot rod
One other thing, if you use a 318 that has smog holes in the heads under the exhaust ports (you'd have to do this on a 360 also), plug them and carefully fit up the drivers side exhaust manifold to the head and grind away the bump till the manifold fits flat.
Good luck!