As i remember from the stone age on my old DT50m the 60cc kit will run with all the std guff, carbs pipe the lot and will give you some usefull extra shove, with some cute gearing you should be looking at 45 maybe. £60 for some usefull go would be a pretty good spend and the carb from a dt50m would be perfect if you can find one, cos they wern't factory restricted (bar the naff std pipe)and have a nice big carb actually designed to run a 60cc motor, try and get the reed block with it cos its the same as yours but with bigger holes.
You are better off with smaller sprockets overall, stay with a small rear and a small front, less torque for the engine to deal with at the output shaft, better sprocket to wheel ratio giving the gearing increace and of course less chain to drag around. If you have the smarts (no disrespect)use the gearbox and primary ratios to calculate the ideal gearing with a target max speed.
I was clocked at 72mph drafting a transit and thankfully back in the day the plod was more interested in how i did it than nicking me, not a lot of point in pleading innocent so i told him and he ended up let me off with a token chewing.
That was on 60cc, tuned so far it was a pig to ride, noisy, expensive (little ends lasted a month maybe 6weeks as it revved a little high ahem) and needed constant tweaks on the mixture. Hot and sunny drop the needle, cold and damp lift it etc. It needed reving to around 3500rpm just to get moving and revved to around 8 or 9. The ig was advanced into the next decade to rev (so it was a sod to start) that high and political promises last longer than the points used to. As far as it goes i recon it had 8maybe 10 bhp on a good crisp day in a power band as wide as a gnats a#se. Fastest thing in Northampton excepting the Kwacs for a while till it got nicked, god i miss that bike.