These are very nice original GM exhaust manifolds that were used on the 1969 Camaro Z/28 models. The passenger's side is 3946826 and is dated A 18 9. The driver's side is 3942527 and is dated C 28 9.
I found these as a pair on the parts shelf of a long time collection that was being liquidated. The dates are a bit apart so I decided to sell them separately. Each manifold has been put up for auction starting at $9.99 with NO RESERVE. Free shipping for paid members in the Continental US. $30 off shipping to paid members elsewhere.
If you are interested, here are links to the auctions:
3946826 RH:
http://www.ebay.com/itm/372412242960
3942527 LH:
http://www.ebay.com/itm/372412246058
Thanks and good luck,
Jason