You defiantly need a tranny. My old 1/8th on road car can pull 100km per hour no problem but it uses a 2 speed to get there, there are even on-road setups that use 3 speed boxes, best thing about the on road setups are that the gears are on the clutch bell so could easily be modified to fit other cars.
Other than that you could look at using a savage tranny coz they have a 3 speed inside them. Make up some modified gears and you could get a massive final drive number with a nice transition zone to get there without killing clutches