I have a 22ft 9ftwide flatbottom handbuilt boat. It has berkeley jet AA impeller and 350 chevy all rebuilt . Moter has flattops 78cc heads and comp cams XM 262 marine dur 218I 224E .460I .477E lift. The moter runs goods but stops pulling at 4000rpm. I would like to see 4500rpm. Thinking of putting 64cc heads to rising compresstion .