Confused on 8.25 pinion shims and location

I`m in the middle of changing out the 321 gears in my 73 8.25 sure grip and installing 3.91s. The factory pinion shims are behind the inner pinion bearing race cup and not between the pinion and inner pinion bearing. I checked the factory service manual and sure enough, that is how they shim it. When you purchase the new gears and master install kit they always give you the shims that go between the pinion and bearing and not the larger shims that go behind the bearing cup? Are you guys just removing the shims from behind the cup and installing the new shims the usual way (between the pinion and bearing), and if so, are you taking the measurment of the old shims and using that same thickness and adding it as a starting point. Its driving me crazy, and I know someone out there has run across this. Just dont want to screw it up, plus its a ***** changing gears on your back :}