Re: which bike to get?
Take a look at what the guys are using here except do get something with V brakes. The vibration the frame mount 2 strokes create might be a source of aluminum frame failure. Steel is safer.
Also make sure the frame will fit your intended engine, which means no full suspension frames.
An old steel- frame mountain bike (big tires, V brakes would be good especially if it has a sus front fork.