To be honest, I agree with the no transmission. If the engines sweet spot is 2000rpm, blower sweet spot is the 1000rpm. Why not do a simple 2:1 ratio to get that, if you need more rpms, give the engine more throttle.
But if you used a transmision wouldn't you need a manual to keep it in gear cause a automatic in OD or D would keep shifting gears every time you get a load. Just like towing a trailer or going up hill. They downshift when they need more torque to do the job. Then your losing rpms which he wants. Only way to solve then would be to put it in 1st or 2nd. But on top of that wouldn't you also need some sort of disk or similar brake system to mimic how you would stop a truck and shift or how you have to have the brake on to shift out of park?? Also don't you lose some power with a automatic??
I think if a transmission was used i would go with a manual. A few needed linkages, then you can solect whatever gear you wanted.
Also there better be a good few shear bolts or slip clutches incase stuff goes south so you don't create a death trap
