Interchangable motors

You can replace a motor in an older vehicle with the same motor from a newer vehcile, but you cannot replace an engine in a newer vehicle with the same engine from an older vehicle. As far as swapping in a different size engine: to make the differnt engine run, you'll need the new engine and matching transmission, the engine cradle and all motor and transmission mounts, the complete wiring harness and ECM from the working motor vehicle. In other words, you can't swap in a different engine without major expense that far exceeds the cost of replacing with the same engine.