974 heads... flow numbers

Nope. The 4bbl pistons will not generate the static compression especially given any available head gasket nor is it tall enough or of the right configuration to generate an effective quench.
While I agree with some of what Dave notes in terms of head theory - most of it IMO is overly concerned with relatively small details that don't add up to more power. You will get more power from the larger valve, especially given the rpm range you're contemplating. If you're really concerned about the shrouding then you can notch the bore but I'd rather not bother. Just my opinon of course.

Yep, put the biggest valve you can fit in there without hitting the cylinderwall before maximum lift.