You can do it on any Crystal gearbox if you want, but using a 12 speed, will give you a lot of cost.
Best is to start with a 40 km/h transmission (the one with 16 speeds and overdrive on the 4th gear) and 20.8 R38 tires.
The 40 kmh version of the 8245 on 18.4 R34 tires had the same topspeed as the 40km/h 16245 on 20.8-38 tires: This was done by changeing a set of gear wheels that drives the main transmission to the rear axle, in accordance with the tire dimension fitted.
You can achieve about 53 km/h when using a 40 km/h transmission, 20.8-38 tires, and a set of intermediate gears of a 40kmh 8245 which originally came on 18.4 R34
If you want to do this on a 12 speed, you need to get a set of gearwheels for overdrive, and change the set of intermediate gears from those of a 4 cylinder tractor.
If you have a 30 kmh 16 speed, you need to remove the 1st gear, move the 3rd gear so that it will sit in place of the 1st gear, and install the overdrive gear where the 3rd gear was.