I never had any problems with offey intake & clifford headers, Clifford intake & clifford headers. MY intake clifford headers/Cut and redesiged to mine.. The Issue is that when a engine goes through it's heat cycle Things NEED to be retorked. I run studs and the stock Clamps with a lock washer on all.
On all my Intake & Headers settups.Once the motor goes throught a heat cycle Or two I retork each time. No problems there AFTER.Useing a MrGasket 155 in/ex gasket with a Skim coat of Copper RTV
I also use a Skim coat of the coper RTV on my collecter gasket as well and NEVER had any problems.