If you have 9:1 now the 68cc heads will put you at 9.78:1. I seriously doubt if it would be streetable on pump gas.
Since you are already close to 9:1 you won't be able to run anything much smaller than a 76 cc head. You might get away with a 74 cc head which would put you at 9.18:1. 72cc heads would yield 9.37:1.
But some where in there your going to run into detonation. The 222 cam will bleed off some cylinder pressure but with iron heads you can't go real high on the compression ratio.