Question on Differential Gear lash

I got a 98 Grizzly 600. There is a whine in the front differential. It is not there when its coasting so I thought I would check the gear lash and see if it is in spec. I didnt think it would help, but I changed the fluid just to see if it would help….. it didnt. It might be the bearings, I have not got into it yet, just trying to get my crap together before I do.

A couple questions about measuring the gear lash. In my CM it shows a diagram of where to measure the lash. It has a dimension "a", but it does not tell what this dimension should be. See image below. Notice that the dimension is NOT from the center of the shaft (like anyone would expect it to be). Anyone know what this dimension should be from the center of the shaft?


Also, is there someplace that I can buy a "shim pack" that will fit the factory gear assembly? The SM shows it here as item #3, but does not give a part number for it.