That would be more believable, you're also going to have to size a cam for it. It isn't just pistons. As T. Neff said, also hieght (equals volume) for CR, and the same with the pistons. 77 CC flow isn't really much, you might take your heads get them ported, or go with a differnt head. Is there any concern with emissions where you are?

 

The smog heads are not worth the effort.But before anything else,this O/P needs to end the guess work on what is which.

 

So was this ever resolved? A "Race Motor" ever built