Are there more than just the one stock racer body or do more appear throughout game play? I don't mean full cart like the egg one or tank but blank bodies like the first cart to start customizing with?
There are a few but its quite rare, my story progress corrupted on me (but not anything else oddly) So i can't tell you how many there are but i do remember there are at least 3
Little King of LBP Level Recordings
You can change the suspension of any kart by going into the Kart Parts page in the "My Karts" section of the Popit. If you want a blank body to work with, select the base "Paper Arrow" body and change its suspension. Once you unlock everything, the suspensions you can choose from are:
Tank (with treads)
The shape of the body will change to match the suspension.