Setting up a 489 with Richmond gears

Post 13 tells you how to adjust your measurement if you are unfortunate enough to not have a carrier that is divided in the middle.
If your housing is not cut in the center get a different housing that is or else compensate for it. You don't have to have $1,000 tool to set up a differential. Good grief.
A parallel, a $50 depth micrometer from eBay and some math equations will get you in the ballpark.