FYI Stealths have that name because externally they look just like a factory iron head. Paint them and you'd have a hard time telling the difference on an assembled engine. Losing ~60 lbs off the top of the engine would be beneficial in an A-body.
But if the choice is only between the 906s and 915s you mentioned I'd go 915, as long as your buddy is trustworthy and you can inspect them reasonably closely before buying. I'd be bringing my valve spring compressor and popping out a few valves to check the guides and seats.
