That cam really should do the job, without killing the low end torque. It's just not that much more aggressive than the stock cam. With a typical CT70 K0, this cam + 52mm (88cc) bore-up kit will deliver high-40s, wearing the stock induction assembly & exhaust. I did see that the aftermarket head has a larger chamber, which reduces compression...we just don't know how much. The valves are larger than stock, too. I could see this combo making the low-end power curve kinda soggy.
As for "continual upgrades"...totally unnecessary, once you get the combo dialed-in. Frankly, you should be close, as-is. The head appears to be the variable, in this equation.
Why did you replace the original head?
A stroker crank would likely increase compression, bringing things back into balance. That's the key to an engine that performs as expected...approaching it as a complete, coordinated/balanced/matched system. I reckon that'd give you more like 60-65mph top speed potential, which should translate into a solid 50-55mph cruiser. Obviously, you don't have to ride that fast. The L125 motor should give about the same power, with a bit more of a torque (as opposed to horsepower) bias.
FYI, I'm not even suggesting that you'd ever take a bike this size onto a limited access freeway. I think more like an engineer and that reference makes a point quickly. A lot of guys become transfixed by top speed numbers and cheap horsepower, overlooking the rolling chassis improvements, i.e. suspension & brakes, to balance-out that increased power. Mathematically, increasing speed from 40mph to 60mph roughly doubles the operating stresses and hp requirement; taking that up to 80mph has the same percentage increases, above 60mph. In that context, it's easy to see how quickly, dramatically, the balance is upset and it's all safety-related. Again, just because you have the power doesn't mean that you must use it...but most red-blooded gearheads just cannot resist. I designed an 80mph CT70 back in `02, when that was quite an achievement. Trust me, even with the requisite braking, suspension and steering upgrades, it's not as much fun as one might think. All of that having been said, here in the upper midwest, there's not a whole lotta grades that extend any real distance. I've ridden a few stretches that were 10% for maybe 3 miles, or thereabouts, had no problem maintaining 50mph...from 110cc. But, I believe that you face some very different terrain and that does make a difference. There's no substitute for power, when it comes to maintaining speed while ascending grades. Your bike has a couple of inherent mechanical advantages over a CT70 or Z50...larger-diameter tires & wheels, longer wheelbase. Those are huge. The biggest challenge may be braking. Drums don't dissipate heat all that well. OTOH, engine braking should do the job. I've ridden on grades in excess of 30% on my CT; first & second gear work very well keeping the speeds below 30mph, on descent...that brakes can take over from there, easily.
From my perspective, of this moment, it looks like 110-125cc is the answer and the cost should be close either way...stroker crank, etc vs L125. The Lifan option is, of course, easier. Maybe you could make an offer on the L125 being offered by one of your fellow members, and do the engine swap on the cheap.
I tried a hotter cam in a 82 ct70 and it made it slower...
