CR Problem?

My engine guy called today.....Good News/Bad News. Seems the porting job on my J heads looks pretty good (good news). Bad news is, he checked the heads for cc volume and found them to be 67cc chambers........which gives me a 12.87:1 CR if I stick with the pistons I'm using. I'd like to, actually. This motor was a screamer before (and I know why now) and ran OK on 97 octane pump gas (leaded premium). I have access to 100 octane Avgas and could run it staight or blend it with 93 octane unleaded. Any reason why I shouldn't carry on with engine assembly?
I've already spent a boatload getting the crank, rods and pistons balanced, and bought the rings.......
This is not a daily driver, but rather, a "Saturday Night Special" car