The switch sounds easy at least from a capacity standpoint. The existing cap = 850#, proposed is 580, and the only real issue is center of gravity. A wheelchair-like device is probably wider than the Hog, so will sit, CG-wise, farther aft but not by much. The Hog CG was over the wheel centerlines & the Gorilla's will be ~halfway between its drive wheels. If 850 times the distance from the face of the hitch receiver to centerline of Hog is greater than 580 times dist. from face of receiver to centerline of Gorilla, then the engineering works. Check this math in both up and down positions.
Another way to look at it would be 850/580= 1.47, or about 1.5, so if the CG moves less than 50% of the original rec'vr-CG distances (either up or down) back from the coach, you're within original design load.
p.s. distances are on the horizontal only, not on the slope, so measure straight out from receiver in all cases, not at an angle up or down.
Baja-tested '08 2-slide 36'
Alpine: The Ultimate DIY'er Project