If it is an iron block it is not a 5.0. If that number is stamped on the engine it is 5.0 alloy block. Easy enough to tell. Look at the top of the block behind the left cylinder head. Number is stamped there.

NADA is not a good source for real world selling prices. Most SL and SLC owners get a good laugh when they see that.

Looked at the EBay engine pics. It does appear it may be a 5.0. The upper radiator hose connection is correct for the 5.0. The hose has been adapted to connect to the 450 SLC radiator. The connection at the radiator on the original 5.0 SLCs is on the other side.