Wow, what a place to start. Everything fresh and the quest of 1hp per cube.
Essentially, the cam is the heart of the engine. The rest is what the cam sends blood to.
With fuel the way it is going to go, I would stay low compression.
An Edelbrock EGR 600CFM carb makes my 350 purr. It is almost a stock rebuild in terms of pistons, valve and porting set up. The cam is Summit SUM1101. That is a .196/.224. After chasing multiple vaccum leaks, and changing the bottom spacer to a four hole spacer, it ran without hesitation, hitting the accelerator was a linear acceleration. Good fuel mileage, gobs of torque.
When I do it again, I would put a quick change timing cover, open up the pushrod channels for 1.6 rockers. Then I would play after the fact.
Mind you, with the SUM1101 camshaft, the engine idles with very little lope. The exhaust tone at idle is distinct hits for each exhaust cycle. With a 2.73 rear, I get reliable 19-22mpg in my van. I can also leave most vehicles in my rear view mirror from a light. This is all at much less than WOT!
I use the performer manifold, HEI ignition. Because I am not removing my heads at this time, I am going with 1.5 roller tip rockers.
A van is much different to change heads than something with an hood. Much more logistics with half the engine in front, and half in the dashboard.
My exhaust manifold is stock, except, I am a gem cutter. I got some drag line cable, injected grit and polished the inside of the manifold through each runner. I do not know if that helped anything except make me feel good as I have no baseline to compare. Headers in my rig is not really a concern. Too much heat. I run 2.5" pipes down each side with a 2.5 Siamese Crossover, I also run the mufflers just behind the manifolds.
Doing it over? I would go with full roller cam, with full roller rockers. Less mass friction. I would also swap out the Edelbrock for a TBI rig, even if I did not have a computer on board.
I have found, some rad is really cool. For a while. Gads, I almost sound like a fuddy duddy, but, I had one of those once, and it got real old real quick. My friends really liked my rig, but, they went out and had fun, and I had to tweak the parts. My van is still not really finished on the outside, but, I get more thumbs up from the rodders here at lights than I ever used to. Mind you, I druel at their rigs. Some are really fantastic.
As a matter of fact, next time I do a build, before I really start, I am going to fly against some of these long timers on this board first, they really take the time to put figuires up that really make sense. I could have saved some pocket change if I had found this board before I started.
Good building. I bet it is going to purr when you are done.