Engine swap to a turbo engine from N/A

Ok instead of rebuilding my old 1987 N/A engine I have decided to just buy a used Turbo engine. I have run across some sites that have some engines available, but they list that this engine is (VIN 2 or 4), what does that mean.

Also, is there any problem with just switching a turbo engine in a car that was just a N/A before?

Any help is appriciated.