Gear Ratio Speed Calculator (MPH)
10/72 with 16" tire, 24MPH, sounds swell for the combo.
GC160 is ok, a smooth, light, torquey, but not a mod-friendly piece, besides the basics.
Leave the governor in place, so no carb swapping to a Chikuni.
It's pretty easy to disassemble and bore/drill/hone the stock carb to a couple more MM of venturi.
The cams break after a while, but cost $6. In a less-than-3600 all day application, lifespan goes up. Pipe and jetting won't lessen life.
Pipe will help, keep it small, long.
A couple degrees advance on the timing does the same as on the more beloved engines.
A better flowing air filter, and jetting up a couple sizes will liven it up.
Stock fuel pump can be removed if a gravity-fed tank is mounted above.
If trail speeds are up, you can do like some of the bicycle guys, remove the fan and shroud.
Air cooled trail motorcycles work fine.
Reducing the fan drag subtracts less of the limited power.
Deeper, the GS versions had ball bearing supported cranks.
Some models have substantially more internal and external finning in the lower case half, for better oil cooling and windage control.
Some have a nice cast aluminum valve cover that polishes up nicely.