Hi there,
basically you're just doing the same as me: putting a new 350 with some performance parts in a van. Check out a thread from a while ago called "cam and CR question". I started that, that has some cam info and it's still active, has some good advice in it. I'm not aiming for any specific HP-number, I'm aiming for high torque low down, which is essential for such a heavy vehicle. But my van is almost only going to see road use, I'm not going to race it in any way. So I won't need RPMs over 4000 much. You can check out that thread and others, chosing a cam is very likely the hardest decision in engine building. Gaskets won't get your CR up by much if you have that much too low from the start. Get smaller heads instead. Always considering you have the cash. What "performance parts" will your new engine get as of now? Is the new 350 stock? Do you have to meet emission standards?
best regards,
Max