Easy. Pull axles. Pull 2 bolts in mustache brace. Pull diff cover. Drop out the whole carrier. Make sure shims stay with each side they came out of. Pull bearing off carrier. Pull drive gear for 4ws. Pull ring gear.
Take axles out of 4 bolt diff. Open 4 bolt diff. Pull the carrier. Pull bearing (without messing it up) off 4 bolt diff.. Pull ring gear. Put 3 bolt ring gear on 4 bolt carrier. Put 4ws drive gear on 4 bolt carrier. Put bearing back on 4 bolt carrier. Bolt 4 bolt carrier into diff, using 4 bolt races and 3 bolt shims. You now have 4ws and 4 bolt rear.
Check diff alignment for peace of mind, but since the carriers are machined out of steel, and to closer tolerances than the cast iron cases, the case is the variable, so the shims should line up the new carrier so your matching ring and pinion still line up right. I've done a 3 of these and they've all been spot on when done.