[Mike C]

I would just buy a quality rebuilt 2 barrel unless you have additional plans for mods to the engine.

The two barrel and 4 barrel heads are mostly the same. Cam is as well most likely.

If you are going to swap on a free-flowing exhaust and do a cam swap, a Q-jet and 4 barrel intake will certainly help add to the package. But just swapping to the 4 barrel isn't going to make much difference and it's all going to be above 4000 rpm.