Junkyard 360 found...should I pass on a modded motor? pic..

$580, not $850. I would bet the holley is a square bore and it has an adapter plate to mate it to the spread bore intake manifold. Lots of good advice here etc, but honestly it is really hard to tell from 2 pictures. If it is not too far from you it is worth seeing first hand, hearing it run, pulling a valve cover, check the oil for water and the water for oil, and if it is all good offer like $350 or $400 and tell him he can keep the holley and rusty headers - they are no good for a car anyway. You can also bargain and tell him that you also have to change the oil pan and pump pick up to car style (center sump). And have a look at the casting numbers and or stampings to verify that it is a 360. It could very well be a 318, or heck, who knows, maybe back in the day someone swapped a 340 in there - you just never know until you look.