Stock 71' Camaro RS head CC size vs 51cc comp ratio

Hey all, new this this forum but here's my first post...I have (father and I) a 71 camaro RS. it has stock heads with 9.5 to 1 comp ratio. If i throw some 51cc heads on there what will my comp ratio go to about? motor is BUILT for forced induction but i don't feel like doing a turbo project like my buddy is. lol. I was hoping I could throw some alum low CC heads on there. what's my best bet? anyone have any guess on 51cc comp ratio or 63cc comp ratios with my current 9.5 pistons? I can give more details if needed. thanks in advance. Steve.