you can buy 1 7/8" headers from hooker, i wouldn't go any smaller with a 406". I run 1 7/8" on my Malibu and have had a 406" and present 377" i'm going to 2"X2 1/8" step headers for the 434" going in it soon. there was a set of 2" coated on ebay recently that would have fit your car, i thought about bidding on them. They went off 2 days ago and noone bid on them, the starting bid was $10.00 with no reserve, but i didn't need them.
Zip.