You can do the fun de-restricting stuff, then you can do some small tapping in the flow of the system by changing out the exhaust (already accomplished) and intake. From there, look into changing the variator, rollers, clutch, belt. A 50cc 4T you are looking to max out closer to 63 roughly. You may be able to push the top end replacing the rollers, but then you could adversely effect the accel to get to the top end.
Welcome to the forum btw.