Thought I'd update this thread on my watched topics with some current sources for the 292 tractor replacement part for this:

http://www.ebay.com/itm/250-4-1-292-4-8-GMC-Chevrolet-New-Exhaust-Manifold-/272464327253?hash=item3f7023b255:g:9scAAOSwB09YOfye
http://www.ebay.com/usr/specialtyengineparts

http://www.ebay.com/itm/400750523442?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT
http://www.ebay.com/usr/reliableaftermarketpartsinc?_trksid=p2047675.l2559