Big time easy peasy. My main motorized bicycle is a 79cc. But on flatground, 30 MPH is pretty easy and probably a good choice for hilly areas. Ya want that low end power.
With mine and folks do say I am mistaken, but I have only disconnected the external governor actuator and have not removed the (internal) governor components. AGK is a member here and has a great how to on his web page to remove it. (Is the gov removal what you mean by "uncorked"?)
With just what I have done, she turns just under 5,000 RPM. On a good day does 40 MPH.
But a major bummer about the HFs (79 & 99cc's) is they are really wide if you put em inframe. You can help the engine up a hill but you dang sure don't wanna pedal one home. But they are both grunt/torque monsters.
I, myself would go with a Honda GXH50 or the HS clone. (Honda first but 300+bucks, last I looked)
With the Honda or clone, much less fabricating needed and they are thinner.
Here is a calculator if you are fabing your own reduction/power transmision;
And this is a build for a 79cc, for thoughts only; (really love the mounting but it slipped)