Steve Heimsoth(heimsoth) found a great replacement part for the Recirculating Ball (RB) steering shaft.
The recirculating ball u-joint is the same as a Kawasaki ATV driveshaft u-joint. The part number is 49050-1055. The genuine Kawasaki one is $35-$50 but an aftermarket one is $14.99 here www.mfgsupply.com/m/c/K158759.html
FWIW, this site has the following dimensions: www.atvworks.com/products.asp?cat=29&pg=2
XUJ300 Aftermarket U-Joint Replaces KAW 49050-1055
Universal Joint for Kawasaki 4X4 front drive shaft. Includes clips. Fits: KLF 300 Bayou 4X4 89-04 Mule KAF620 2510 4X4 A1-A5 Crosses to Kawasaki Part# 49050-1055
Dimensions: Cap - 16mm. Width cap to cap - 40mm.