How can you determine what year an engine is?

We have an 83 Olds Delta 88 Royale. The engine in it is not an 83 Delta engine. We do know that it is a 307 with 7A heads. That gives us between the years 85-90. Anyway, we need to replace the MAP sensor, but we can not identify the engine to get the part! The parts store is no help at all. I do not believe that it is a Delta engine at all. Possibly Toronado or Custom Cruiser. Does anyone know how to find out what year and what it might have come out of? Thanks all!