If you want to use the Self Locking difs, or the adjustable difs on a FG Off-Roader you have two options.

1: Get the rear dif Raiser blocks (#4478)
2: Cut a grove in the plate for the ring on the diff, just like there is one for the gear wheel.

I have the Allu diff.(#8483/5) on my FG Leopard. I plan on putting in the 2 way self locking upgrade(#8497), someday, when I get the time.

Or maybe if there is a good one on eBay, I will try to get a 4 way self locking diff.

Happy driving from Greenland
Jesper Rex