There's a pair (3780730 and 3790729) on ebay by seller rnchwgn. They are for a non-air conditioned engine. The seller is kind of proud of them. Manifolds pop up on ebay from time to time with a wide range of prices. Search 64-67 Nova L79 exhaust manifolds. I have purchased two sets off of ebay over the years and didn't pay anywhere near $750. I've heard that 70's model GM truck manifolds will also work. Maybe someone on the forum can confirm that.