You'll want a 100V system with a 100A controller. You'll need some seriously thick wiring to handle that kind of discharge current, and your battery will either have to be LiPo (prone to fires, hard to charge properly) or will have to be composed of 20A/25A/30A 18650 cells, which are expensive and tend to have less energy density than other cells.
The easiest way to go about it would be to contact Kinaye Motorsports in Seattle. They'll set you up with a MXUS (3000W-rated) direct-drive hub motor, a beefy controller, and a battery that can handle 6000W+ peak output. That should get you close. Their bikes will definitely hit 40MPH and perhaps 50MPH. If you want to go faster than that, you might have a pay a bit more.
Another good motor option would be the QS205 hub motor laced into a 17" moped wheel. I've been told that some QS motors can handle 10000+W.
Any ebike capable of hitting 75MPH would probably weigh at least 85 lbs, if not more.