Denny, keep the 216. Factory Chevrolet, bolt-on, VCCA Approved and it did a great job during World War 2. We won. I'm not sure if this quick procedure would help, but.. perhaps it worth a try, have you re-tourqued the cylinder head bolts? Could it be a leaking gasket? What about magna flux? If you pull the head, this could be cheaper than X-ray. Just my two cents.
Dale