The valve problem was probably caused by the valves being open during the time it sat and rusted and are not seating now,I bought a 55 olds that had only around 5000 miles on a rebuild that sat for 7 years and it had one exhaust valve that did not seat properly. A simple home valve job should cure the problem and if you need any gaskets I think I have a set for the 216 which you can have for the cost to ship,I think the cork gaskets are shot but the head,intake/exhaust and other gaskets are good.

1937 Chevy 1/2-ton pickup