I’m installing the slip yoke eliminator kit onto my 231 transfer case and have found that the replacement main shaft is larger than my old unit. I can not reinstall the roller bearing back onto the shaft; did I get the wrong kit?

The slip yoke eliminator kit you have purchased has several improvements made to the unit including the main shaft that make it stronger than the parts you are replacing. The kit comes with the thicker main shaft that does away with the roller needle bearings all together. These parts will not be needed as stated in the installation instructions.