no mate, i think you are thinking of the front where the pinion climbs the crown wheel teeth because the casing flexes

resluting ni the thick walled casings available form various leading providers of thick walled ford front diff manufacterers

in the rear you either live with the 7.5 inch diff (you've got the 7inch one) or yougo up in size to a 9 inch of a jag diff, the bits that you can uprate aren't the pinion or crown wheel

with 400 brake and rwd i don't think you'll give it nightmares, but a step up to the 7.5 inch diff (you'll need the 2wd shafts and outputs etc to go with it if you want to upgrade to the 2wd cossie stuff) would be the next step up from the likes of a granada (the 24V has an lsd in it)