I wouldn't want a TJ or JK frame/suspension. They use coil-overs and wouldn't be much fun to mess with for any sort of conversion. They don't even work well for jeep guys wanting to do lifts and mods. I would look for a YJ frame/suspension. The YJ used leaf springs on all 4 corners like a CJ, however the YJ uses a full-box frame instead of the CJ's c-channel frame. The YJ also has a wider track width although I imagine you probably wouldn't be using the YJ axles anyway.