What you really need to go 70 is a Euro model 'moped' that has better brakes and suspension and is built for more speed in the first place.
To take a US spec ped made for 30mph and make it go 70 is asking for trouble
(engine damage and personal safety).
Motorwise it takes a complete rework of the motor...
air filter/carb/reed valve/cylinder/piston/head/exhaust.