Hey I recently bought some GT40's that were from a marine application from some one claiming they were 64cc heads. I kinda thought the 64cc was stock chamber size but I looked at the chamber and it doesn't look like theres a lot of room to equal 64cc. Might be 58cc. Anyway you can check by eye balling it or while the heads are off the car? Will porting them open up the chamber enough to make a difference? I'll post a pic later today of them.