Elvero; I have a 48cc (AZ street legal) 2 stroke Chinese engine mounted on a chromo steel mountain bike frame. It has no cool factor, but it is great for errands and commuting.
Engine mounting plates look fine and are available on EBay. (Check out the stretchers and choppers in the photo gallery)
Two stroke engines are cheap (about half the price of a 4 stroke) and look like a motorcycle engine.
4 stroke engines don't require mixing of gas and oil and are generally quieter.
Electric motors are quiet and green, cost about the same as a 4 stroke, are very heavy (batteries) and usually have less range than petro bikes.
I just moved to south Gilbert this weekend. There are 5-10 riders on this site from AZ. Tucson riders are very active and post group rides often.
If I were you, I would start by viewing the photo gallery (all of it!) to figure out what you would like to do. Then visit the engine mounting and engine troubleshooting forums to figure out how to do it. LOL