Ok, so common sense aside, when you say "back the gaskets up", do you mean put it behind them to make them smash up against where they need to seal or put pieces of this stuff where I believe it to be leaking at. Specifically the corners.
1968 Firebird 350|#17 Heads|Cam identical to 350 H.O. specs|Holley 650DP (mech, secondaries)|Edelbrock Performer Intake|Manual 4 Speed with 3:73 rear