I just want to add to this thread because I could not find it anywhere on the internet:
2021 Woodland Mills WC46 + 2020 Kubota BX 23S = a stock PTO shaft trim of 9 (NINE) inches!
Every video I watched was either 1/2 inch or maybe up to a few inches. I was so worried I got my measurements wrong I measured 4 times.
Stock factory shaft = 29 1/2"
Slot to slot from tractor to chipper = 21 1/2"
+1" per the instructions, cut and fit, seems to work fine, although I'm stuck back here at work before running it.
Note: In fitting this shaft I would have realized if I did NOT measure and just tried to fit it on there without measuring, there is NO way it would have fit, it had to be trimmed a LOT.