z50chopper,
Click
HERE and you'll see that the ATC70 doesn't have a conventional trike or quad-type swingarm.
To follow up on that trend of thought, the Xtreme Typhoon 125cc quad has a swingarm setup that, I believe, is bolted to the frame of the Xtreme CR3 dirtbike. You might want to look for one that has been thrashed on eBay or craigslist, take the whole rear swingarm assembly and look for a decent newer
XR/CRF-style frame to do a custom build. With some fabbing skills and the right tools, putting it on a
Z frame would be quite the challenge.