Well, you wanted 2000 lb ft torque on the auger. Wouldn't the auger have to be direct driven by the gearbox in front of the fan? I don't think those cast iron gearboxes will handle that kind of power, but I'm not an expert.
[I'm leaving this thread here for now because I don't know of an elegant way to move it all to Snow-Removal]
No, the reason for the gearbox behind or in front of the fan is to provide a turning shaft to drive the chain sprocket of the chain reduction for the auger. These gearboxes provide reduction for the fan ONLY on the more powerful sets, for reasons I don't know. On lesser hp rigs like my current one the 'gear' box is just a through-shaft to the fan with the mentioned side-shaft. I don't intend to use gearbox reduction as-such for the fan itself at all, unless I learn something new.
The current rig offers some 180 ft-lbs of flywheel torque, that gets first multiplied by 2.5 at the belt reduction to the fan gearbox, then the otherwise unreduced side-shaft drives the chain sprocket where a FURTHER reduction of around 3 takes place. I don't know the math to determine how much of the 450 ft-lbs arriving to the fan gearbox finds its way to the chain drive. I think all it of when the fan is unloaded, over 1200 ft-lbs, which then drops as the fan encounters load, falling to nothing when that load starts to stall the engine. Now, since the side-shaft driving the small chain-sprocket is only 1-1/4" it's obvious that the John Deer engineers never expected all the torque to reach the chain-drive. Ant that's OK because in the original concept it would have been impossible to point the auger at the frozen ground and load it to death. In my setup it IS possible, AND it was intended to be possible, and it IS used.
Now if I were to place the gearbox to serve the sauger system in front of the fan, its sole purpose being to supply a 3:1 reduction chain-drive for the auger, then the torque leaving that gearbox would not need to be more 1/3 of what reaches the auger, let's say 750 ft-lbs to get 2100 at the auger. This would make it a smaller (and lighter) box then the current one using 1-1/2" for the through shaft and 1-1/4" for the side-shaft.
I fooled myself into thinking that I could get away with the downsizing, and I could too if I kept the current engine, but if I seriously raise the power then the potential torque reaching the auger will rise in direct proportion. That's just wonderful but I have to keep in mind that even the proportionally less torque arriving there will then be far greater than the current 'total'.
That's about as best as I can sum it up. I saw some skid-steer augers driven by what looks like otherwise unreduced hydraulic motors. But as my nose has been rubbed into it by i forget which expert here, getting a 2000+ ft-lbs dedicatred motor would just open another can of worms so I think I best stick to the much lighter-weight chain drive and reduction even though with more power that too will have to be beefed up AND wil require a gearbox at least equal to what I have. What remains as a valid flash-in the pan from my idea is to put that gearbox in front of the fan which doesn't need it, THIS would allow a smaller box than one also servicing the fan even with just a through-shaft. I'm now putting about double the design torque on the original gearbox, it's holding up good, but I'd be pushing it with as little as maybe another 50 hp on tap.
