Doing a head swap, need some info.

Whats up? I have an 87 325e with the 2.7(ofcourse) and I plan on swapping the head for the 2.5. I've heard that it's basically a direct bolt on and i would need to the donor motor, the ecu, the wiring harness, and prolly new gaskets and head bolts. My questions to all you guys is where can i get a complete used motor for a decent price? Has anyone ever tried this? What else am I going to need? Which head from which motor would work the best? I'm mechanically inclined and so are most of my friends so we will be doing the swap. Right now im just in the process in finding out what this is going to require and how much its going to cost. Thanks for any response what so ever!

Rocky