I am going against the grain on the cam choice. I say stab the Comp 265DEH in it. It will have a noticeable idle and increased performance and works great with stock exhaust.
On the stock exhaust note (pun intended), I would recommend to run dual exhaust minimum, if not add an h or x pipe.
The stock single exhaust pipe on a 318 is the biggest restriction on that engine. At least put a 2 1/4" dual exhaust on it, it will wake it up and let the 4 bbl breathe like it should.
Nothing wrong with using the stock exhaust manifolds if you wish, just hang dual pipes on them....
When I put a dual 2 1/4" exhaust with an h-pipe on my stock 70 Dart Swinger, it really woke it up, especially from 60 - 100 mph, even with the stock 2bbl carb...