Standard mods for more power are a bit of machining and an extra clutch plate in every pack, stronger springs in the accumulators, and then boost the hydraulic pressure. it's just how long before you have to throw more clutches in... but clutches are cheap...
The piddly little gears might be the long term problem, or the welds between the clutch housings and the shafts.
Probably better to buy an aftermarket box made for the job.