Bikeguy Joe
Godfather of Motorized Bicycles

rockshox are good, you want motorcycle triple clamp type forks if you can afford them. what he meant by springer forks is the old style forks that are junk except for looks. the engine you link to is way over priced and under equipped, i would buy an old dirt bike and use the engine because it will have replacement parts and at least a 3 speed transmission. you will only get 60mph out of that engine if you dont mind extreme rpms and short engine life, thats why you need multiple gears. i would suggest an older 4 stroke for authentic chopper sound.