Flowtech headers, edelbrock performer rpm, QF 4v carburetor, and a distributor recurve and my stock "ish" 390 is pretty darn peppy.
I don't know what kinda power numbers, and I don't really care.
At the idle-4000rpms it's a very well mannered yet powerful engine.
Bingo, key to a happy low budget truck. headers, a nice exhaust and a distributor recurve first, intake and a good 4 barrel second. I personally don't think the cam becomes critical until you can get inside and see what you have.
If it is a budget work truck, and a C-6, I'd go shift kit third to get it hitting hard and living long.
If I had to guess, 35-40 hp more at most, but the entire curve would build and feel much stronger.
The only caveat, IF you live in an area that you expect all the manifold bolts to break due to rust (most everywhere) and you aren't going to use a torch to heat the top ears to get them out. AND the truck is worth the extra money, consider biting the bullet for Edelbrock heads and FPA headers right off the bat.
It's not logical timing in terms of power, but if you are going to break 5 bolts, have the heads rebuilt while they are off, then later try to make bigger power later, buying the FPA/Edelbrock combo now will save you some headaches and allow the entire swap to be a weekend project. Easy to spend someone else's money, but it depends on your goals
Certainly outside of what you asked, but a consideration, saves you from buying 2 sets of headers or paying a lot of machine work on the heads
