That is an honest, but heavily-loaded, question. I am not being a smart ass. With bikes this size, what seems like a small dimensional difference can have a big impact. For example, a +2CM swingarm (on a CT/Dax) is enough to result in tire-to-fender contact and make the wheel appear slightly disconnected from the frame, unless a taller tire is fitted. +4CM and longer look ridiculous. The most obvious difference between the CT70/Dax frame and ST90 is in the motor mount area, the latter is substantially longer. Only way to get definitive answers is to place the two frame side-by-side and take accurate measurements. FWIW, getting the wheels positioned so that they fit, visually, should give you most of the CT70 aesthetic. That should take little more than a shorter swingarm and fork legs.