I bought a 2wd roller off CraigsList and the guy hooked me up with a ton of other parts, including another bare chassis. Can I use any of these parts to start a 4wd build? I'm not sure how much is shared between the two platforms and if it would make sense $$$-wise or if I'd be better off just buying a 4wd roller. Really my only concern is $$$. I have the time to learn and make sure everything gets put together correctly, I just don't want to break the bank doing it.