Large shims go inside the gearbox case on the outdrives, against the bearing, I'm guessing the smalls one go on the end of the dog bones / axel inside the rear hub. The MIP B5 ball diff is about 4 mm narrower than the B6 ball diff. The B6 also has 2mm shims for the gear diff that you can use with the MIP unit. Associated also has a diff shim part # 1733, but they are really thin, might work out on the hub side.

Just built my B6 with B5 MIP bimetal diff, spacers from the gear diff, no spacers on the hub side yet. I think it's going to be OK, at full droop the flats on the puck are fully inside the outdrives. Hobby shop was out of PN 1733 so I will add when they come in.