Great tech tip, Grigg. Wish I'd had that several months earlier!!!

You should check your linked pictures of the clamp plates, though. They both reference the 10-hole rear plate. Do you have any idea as to their purpose? Added strength? Or why the 19.5 wheels from P30's and 3500HD's have clamp plates with chamfered holes and conical lug nuts? Since they're hub centered, I would think you could just use washered lug nuts directly on the wheels like you show on your 22.5 wheel.

Also, as for the metric tire sizes....the way I understand it (and I'm pretty sure I'm correct), is that in your 245/75R22.5 example, the 245 refers to the tread width in millimeters, the 75 is the aspect ratio, R is radial, and 22.5 is the wheel size in inches. (Why they combined standard and metric is beyond me).

The aspect ratio means that the sidewall height is 75% of the tread width (75% of 245mm is 183.75mm). 183.75mm is about 7-1/4 inches. So, you add twice the sidewall height to the rim diameter to get the overall height of the tire----- 22.5 + 7.25 + 7.25 or about 37 inches. Again, why they combined standard and metric is anybody's guess.

So, that means that if you switched to a 245/50R22.5 low profile tire (if there is such a size), the tread width is still the same (245mm), but the sidewall height is now only 50% of the tread width, so the tire is much shorter. To maintain the same overall diameter, you would move to a larger rim size.

One more note...The 8R19.5 tires on my donor truck measure 33-1/2 inches tall. The old 6.50x20 are also 33-1/2 inches. 7.50x20 are about 34-1/2 inches. So, for some folks with smaller original tires, the 8R19.5 might not be such a bad swap (if they clear the brake drums).

Hope this helps,
Bob