In 1967 and 1968, Firebird 400's had a limited secondary opening, easily fixed with a pair of pliers. When corrected, Firebird 400's always outran GTO's in side-by-side tests, due to their lighter weight and better flowing exhaust manifolds.

There was no "upgrade" to a GTO engine, the Firebird 400 and GTO used the same components, just different part numbers for the assembly process.

Back to the original question....you have a transplanted 1969 GTO engine in your 1968 Bird. Nothing to be embarrassed about at all, unless of course you paid for a matching numbers Firebird 400.