This has been raised before in various forums and Oldsmobile enthusiast websites. The answer is "there is no difference in the chassis between a Cutlass S and a 442 that would preclude you from using the same headers". It is a marketing decision on the part of manufacturers, what gets a bigger bite? Advertising a performance part for a 442. Even though that same part will fit other models of the same year for that chassis/body style. If you want more info on this answer go to Realoldspower.com and do a search for "headers" you will get a lot of hits but it is in there, I have read numerous posts asking exactly the same question you have. Good luck on your build.
edit: I just did a search over on ROP and found this, one of many examples;
http://www.realoldspower.com/phpBB2/...hlight=headers
I also amend my post with this caveat, you MIGHT need to get a transmission crossmember with two humps in it for dual exhasts if your car has only one hump and originally came with single exhaust only. I think that some models were like that. You will need that crossmember anyway regardless of what headers you end up with so the exhaust pipes will fit well under the car.
[ January 20, 2005: Message edited by: Oldsguy ]</p>