I'd think it very easy for Westfield or any mfg to supply a heavier gearbox. The shaft sizes could be adapted to just about anything..I think. One shaft has to support/drive that chain coupler. If the coupler (needs proper # of teeth & pitch) couldn't be purchased w/proper shaft size, then it could be welded to a hub that would fit the shaft. You'd want to make sure it was welded "true" however.

Same with the pto shaft on the other end. The vertical alignment of the gear box is done with those 4x 1/2" bolts they weld on a plate. Plenty of room there for more substantial gear box.

I'm not sure I'm a believer in this "critical alignment" thing. If it were that critical, I wouldn't think they'd use a chain coupler arrangement. Also, the gear box runs just fine on smaller electric drive augers. It uses the same chain coupler & the whole thing is just bolted to the top of the auger mount. Doesn't look "critical" to me. Yes, you might wear out the chain or sprockets prematurely, but certainly not break the shaft....repeatedly. By the way, our 2 broken gear boxes showed little or no chain/sprocket wear. We kept those same components.

Robt in Cen MO, I'd sure never put that drive on a 10x81...not HERE!