400 budget compression HELP +++++

Quick question for all, being it is a low compression 400, how much can he increase the ratio with a head swap?

What could we be looking at? A 1 point gain? Better? Less? 90cc head (?) down to a 75cc head (OOTB State) equal 1 point?
This would be a 7.8-1 stock ratio (?) to a 8.8-1 or possible 9.0-1?
Just wondering out loud.