I need a bit of help from you guys, I am looking to buy a set of Blue Thunder 64cc heads with chevy style exhaust ports. does anyone know if the valve placement is the same as my D3s or will some "custom" pistons be in order. I ask this because I am building a new engine for my 21' barge and was thinking about a ~520in engine. I guess what I was really looking for is will the "out of the box" pistons work or will some fly cutting be in order. advertized lift will be under .600. thanks for any help or suggestions