I need a new engine for my 96 Monte LS. It currently has a 3.1 in it and I am looking at buying a 91 Lumina with a 3.1. I understand that some engines, even the same types are set up differently and will only work on certain cars. Is the Lumina engine set up correctly to just drop it in my Monte? I can get the Lumina very cheap and it does run currently, so should I take the car and use it to put my Monte back on the road or should I continue to look for another motor for my Monte?

Absolutely not an interchange, check with a salvage yard for their listed interchanges.