My K3 does 125 mph (maybe only 120 on a radar-gun) with stock pipes, 120 main-jets, a K&N filter in the stock box, and 1-over pistons on a fresh bore. I lapped the valves but otherwise the motor is stock. The final drive is 18-43.
So, you want to go at least 125........spend a few hours on the High Performance page.....Dozens of pros have offered very good advice about building reliable power for the street with these 'old' bikes.