How Much Can Heads Improve Compression???

Instead of trying to guess what heads to use, first measure where the piston is at TDC, write it down, if the pistons have eyebrows, id the piston volume of the eyebrows is a catalog spec, write it down, get a measure of chamber volume of the heads you have to choose from, write it down.

Figure out what you want for a compression ratio when you are done, calculate, using the information you have written down what your possibilities are with chamber volumes and gasket thicknesses; then you'll know how much you can incress your compression ratio.