Try these guys : http://www.ramairrestoration.com/pontiac.html?cat=12 They make good quality factory headers for the American Pontiac ...

The factory style manifolds that are being reproduced are probably nearly as good performancewise as long tube headers but without being as prone to leaks. Headers are the ultimate, but they can be a pain to fit on a Pontiac and may need a few rounds of retightening to stave off leaks. I remember years ago my friend was looking for headers for his 1973 Firebird with a 350. The guy at the speed shop told him Doug Thorley was dropping that Pontiac application, perhaps due to the lack of popularity due to the pain to fit them and the relative ease in fitting the Pontiac performance manifolds. Seriously, I remember Pontiac Enthusiast magazine testing the manifolds and found they gave very good performance when backed by a decent exhaust system.

My advise is to not rule out the reproduction Pontiac performance manifolds. Repro 421 tri-power or 428 H.O. manifolds should get you where you want to be.

IIRC the Pontiac manifolds don't use gaskets either, except for possibly the aluminum early 1960s Super Duty museum pieces.

Would these work for you ? http://www.ramairrestoration.com/lb-1-long-branch-d-port-factory-headers.html I like 'em !