Check the front motor mounts- - - -if they're straight across from each other, you've got a late model 250. The mounts are offset on a 292, and the side cover would also be very tall. The valve cover with all the oddball plumbing and the air injection lines in the exhaust ports pretty much date the engine to the late 1980's or so. Does it have the integral intake manifold cast with the head? Hope not, as those things were bad when they were new, and several decades of use haven't improved them! The 4-BBL was never a factory option, BTW, that has been adapted somewhere along the way, and probably isn't calibrated for a 250 at all. There was a Q-Jet for a Pontiac 250 overhead cam six, but it's about as easy to find as a saddle-broke unicorn!
Jerry
