If your handlebars incorporate the same internal throttle assembly used on the CT70s, there's enough travel to work with up to a 22mm carb no mods required. The cable may be another story...inner cable stick-out length. That can be altered. If it's too short, a coil or two of outer sheathing can be clipped. If it's too long, then one of the end ferrules will need to be replaced, after cutting the inner cable to the desired length.
Best place to begin...install the carb, twist grip throttle assembly and cable and see if the slide will go from closed to fully-open.