I see what your problem is now... If the new gearbox = 20 spline = 1000 PTO. Won't work the gearing isn't right.
Sounds like all you need to do is repair the diverter box if you can get a replacement shaft then get a full set of slip clutch to Shearpin adapters for the PTO shafts.
Do the final drive shafts also have the same shaft/shear pin setup?
What you have going on sounds like a PITA. I also hate a shear pin.
If you look on German Bliss who carries Rhino parts you can probably find the replacement shaft you need but goes by the Serial #.
