Countershaft bushings in an 833 OD aluminum case

Has anybody done the steel bushing insert for the countershaft into an OD trans. Can you buy the bushings or are they something that must be made by a machinist? Anyone have pictures and dimensions? I heard it is not a hard mod to do but just wanted to get other thoughts on doing the upgrade. I am probably going to buy the Passon OD 18 spline gear set and want to modify the OD case I have before I assemble it.