The 346 heads are open chamber heads. The 383 was actually quite lower in compression then advertised.

The easiest way to get compression is go to a closed chamber head. So with that being said it is worth it to spend some time trying to find 516 or 915 heads. The 915's are the better choice, but are a bit more rare and can be more $$. the 516's work fine though.

If you do not go with closed chamber heads then you're left with boutique pistons or a lot of machine work...or both.

Everybody here is trying to help get your goals but you need to be realistic of the costs and effort needed to get there.