Don't forget to derestrict your muffler----it was a weld-bead in it & needs to be filed smooth. Keep your shop-vac on hand to help prevent shavings going into the exhaust---doubt it matters but I kept mine very clean throughout the process.
If the temperature in your area exceeds a 45-95 degree temeperature range, then you will definitely want to consider getting a few different main jets for your carb. If you ever increase/decrease a main jet by more than 2 sizes, also increase/decrease the pilot jet size by 1.
IMO, a 1987 CH150 should be hitting 60mph no problem, with a few simple mods. untouched & fully stock, yep 58mph is about an ideal top speed. You should be experiencing almost wheelie-popping torque off the line, though, even bone-stock.
Something also i have noticed regarding lagging performance: I put SLIGHTLY LESS than the recommended amount of oil, IMO the recommended amount seems too much & can be slowing things down. Consider a lighter oil as these scoots don't really run very hot anyway----i switched from 10w40 Pennzoil to a 10w30 Quaker State & I do notice the difference. You may also need to change a laundry-list of bearings also, CERTAINLY your wheel bearings; a bad wheel bearing will cause lower top speeds & will make your engine work harder for nothing. The integrating bearing on the driven face was shot on my scoot, caused me to snap a driveshaft, whilst replacing ALSO found some bad bearings inside with the gears. ..
VERY IMPORTANT!!!!! When you change your tires ALSO CHANGE YOUR VALVE STEMS! A new tire is nice & safe but if you keep the same cruddy, weather-beaten valve then you risk that sucker blowing out while riding. . .not good.
I'm actually SURPRISED nobody mentioned anything about bearings up to this point. . ..!