Two strokes are real interesting little buggers to make go fast... and it is based on a lot of interesting phyics principles... (in my opinion).
Here is a site with a whole lot of good engineering and science info.
Take a few days to read what you can.
The 2 primary things to gain HP are the cylinder port timing and size... and the exhaust pipe dimensions.
Next comes intake flow and size and compression ratio.
If you undertake to do these mods yourself you will probably seize and blow a few motors... but you've already said you don't mind.
Having only a 2 speed limits the mods.
Because many of the mods narrow the power band.
And raise the RPM (which the motor is not built for).
I'm guessing that with a little money and time I could make one of those go 60 mph without too much trouble.
No promises on how long it would last.
I'm planning on that this summer with one (Suz FA50...maybe not 60 though...45/50 would be OK...single speed)
There is also a message board there... check it out.
The board has a forum for small bores.
Make sure to open the time window for older posts.
A lot of the people and questions and answers (on the board) are misinformed IMO.
You have to read with that in mind.
I have a couple other good sites also when you want.