The 3 bolt 292 exh manifold is available new. Here is one on ebay.
https://www.ebay.com/itm/250-4-1-292-4-8-GMC-Chevrolet-New-Exhaust-Manifold/283068812437?hash=item41e8374c95%3Ag%3AayUAAOSwP79bVdfy&_sacat=0&_nkw=292+exhaust+mainfold&_from=R40&rt=nc&_trksid=m570.l1313
I would also suggest going to your local exhaust shop. They will have the flanges in stock if you really want to do the 2 bolt flange.
