I didn't take your requirements as an insult to Shercos or any other modern bike Chewy. Thing is modern bikes are designed for modern sections. The motors are designed to be a small as possible which limits things like additional flywheels (which I suspect is what you need). Can they be improved? Well yes but only, IMO, marginally. Detail stuff. But to change the character of the bike from a modern piece of tackle designed for modern sections to something that would have been appropriate, say, 30 years ago I have my doubts.
As an analogy it would be like taking a formula 1 car and modifying it to be a convenient city runabout.