I WOULD LIKE TO USE IT AS A DRIVER. I HAVE A 200R4 OD TRANS FOR IT. WOULD THE BIGGER VALVED HEADS LOSE MUCH MILEAGE? WHAT HEADS SHOULD I LOOK FOR? I HAVE A FRIEND WITH A FEW PONCHO HEADS LAYING AROUND THAT NEED REBUILT. HOW MUCH SHOULD I EXPECT TO PAY FOR REBUILD OF HEADS?