I got one step closer to putting the snowblower on my 522xi. I replaced the flaky old PTO clutch (which slipped intermittently when it was warmed up) with a new aftermarket unit. As far as I can tell, the build/fit/finish looks as good as the old clutch, which I assume is the original, since the machine had very low hours on it when I bought it years ago. The only difference I noticed is that the new clutch hub doesn't extend as far forward as the old one, making it a bit harder to get a good grip on it with a 1-1/2" wrench. The new clutch came with a 1/4-inch-thick washer to make up for it (based, I suppose, on the assumption that the user would install a replacement bolt of the same length as the old one), but instead of using the thick washer, I opted for a 1/4-inch shorter replacement bolt of the same grade as the original and torqued per the service manual instructions.
After installing the clutch, in hindsight it occurred to me that I 'might' have been able to swap the old hub for the new one to make it easier to get a wrench on it, but it's in now and working fine, so it will stay that way.