it sounds like your on a budget so go for a 9L motor, 3s lipo, use your mm, and get a ccbec. gear it for about 35 to start with and go from there.
btw mike can make you a mount, if you send him one of your center diff mounts, as for a battery tray you coul use one off an emaxx, use an rcm tray, or make your own.