Somebody correct me if I'm wrong, but block cylinder size, head chamber size and camshaft are the 3 biggest items for planning an engine. Higher compression gives more horsepower. Lower chamber sized heads (like 72cc) give higher compression. Higher compression increases heat increasing the need for higher octane to prevent detonation. About a 10:1 compression ratio can be run on pump gas. 72cc on a 400 will give you about 10:1 compression. 92cc on a 400 will give you about 8:5-9:1 compression. Higher compression allows the use of more aggressive cams which can add more horsepower. Ideally the #16 heads will give you more horsepower. But if this is your first build, practicing on the #15 heads would be better IMO. Whatever mistakes you may make from the first engine build, you will make your second build better.

The camshaft can get pretty technical with the math. Read the posts in the Hall of Fame about compression ratio. I think it simplifies it more. You could also try a dyno program to see what works and ask others what cams they have used. Some camshafts are considered better quality than others.

If you are comparing engine building plans in the back of the book, use one that is comparable to your heads and block. I'm guessing you will probably make some changes along the way to make things work.

I really don't know much about the HO and Ram Air so I can't help you there. They are good heads but I'm sure they get a higher price and are harder to find too.