8 3/4 gears

If it were I doing this, I would do much like Ricks70duster340 did.

All 8-3/4 center sections will swap out between each other. Only the U joint size max hinder a otherwise quick and easy swap.

I have used the Dr.Diff upgraded axles on green bearings & a currently sport a 742 case. I like the bigger 7290 U joint. Your driveshaft is probably the smaller 7260. Ether a new driveshaft or the cross over U joint that has the big and small sizes on it already.

All the rear disc brake conversion kits I have seen require a 15 wheel.
All the axles upgrades I have seen are on the larger 5X4-1/2 bolt size.
This leaves the front at 5X4.

IMO, there is no overkill here.