I have a Offy 4 barel manifold that I want to use on my 65 292. It is plumbed for heat. The inlet and outlet are 1/4 and 3/8 pipe thread. 1st question is which is which? Question #2 is if I want to use this with a stock exhaust, minus the heat riser, is there a plate I use between them to keep the water from running into the exhaust. Thanks