The rears are about 1/2" wider than the TT wheels and a 1/2" shorter in diamter. Those are rough eyeball measurements of course.
In all honesty I don't see how 4 fronts could handle better....less tire to grip the ground. What 4 fronts gives you is less rotating mass, and less strain on the steering servo. With 4 fronts on the chassis can roll more inparting higher pressure on the outside of the rims. It gives the feeling of better turning but can dig in and catch causing a rollover. Id rather sacrifice a little rotating mass and keep the consistent handling characteristics 4-rears offers.
As far as the conversion goes, it was an MT Pro originally. I ordered the rear wing posts, the rear wing mounts and the rear wing itself. Some slight modifications had to be made to the MT rear bumper bracing and the wing posts. All in all its pretty easy to do. After that I followed what Kryptonite did on his to lwoer the body.
I finally got everything stiffened up like I want and am going to giver her a go this afternoon. I added Forists chassis braces (man they rock) and a new head gasket. Now maybe I can see what this 29cc OBR can put out with the side dom.