carmine,
Here's an elderly thread about gaskets creeping:
390 problems | Capital Area Cobra Club
It has been a problem with lots of different engines, 351, 385, FE and so on. And if you search on Print-o-Seal you'll probably find other photos of the same problem, different engines.
The solution is to use only gaskets with a steel shim sandwiched between the gasket surfaces for street engines. Even the gasket maker admitted this was a problem.
Just using the gaskets for racing proved OK since they were replaced frequently. Street use with many more heat cycles resulted in creeping, allowing gas and water leakage to occur.
Bottom line: use the reinforced gaskets for street!
Tom