The ST45 is your rocket of choice. Mac's makes a pipe system for ST and yes it won't fit OS 46 clones. I have bought chinese replacement parts for my Italian ST 's and they fit fine. The ST carb is great and was the choice of many other brand engine users if they fit. I think the ST has a little more low speed torque. A ST will run lean when others would die in a split second. If you set the ST with a tach on high speed you will get a screamer. Don't be afraid of the chinese ST. The ST will get a couple hundred RPM compared to TT.