68 and up 318's and 273's should be 675 open chambers. 8.8:1 is not bad with available gas today. If you want to go 318 I'd build it like a 340. Pistons and 360 heads, copy everything a 340 had, then you will have something. Only you won't have enough tire under an early A. Get the right cam and set it up right, degree it, in the 273. Then have at the 318 whatever you want. Forget the Erson, Call and get a custom cam for what you want to build. Then you will be happy and done.