You want the ’54 – ’55 303467 base gasket, not the 304314 one. Using the later one will give you an internal cooling water leak. The motor will have lots of water at the flushing port but will be leaking into the exhaust housing on the inside. Your CD-12 must be an early one with the thumbscrews on the hood and a flushing plug installed.
Here’s the two different gaskets for comparison. The 303467 one is the top one.
