I dont think theres any writeup on here, maybe ... ive never looked.
Basically, it's a pain in the butt. Only because you gotta drop the transmission and as many times I've done that, I still hate it LoL
you're gonna need to replace the real oil retainer seal (i dont remember if the rear main seal comes with that in the package or not, i forget, i dont think it does. And a 'speedy sleeve' might be a good idea. It's a slip that goes over the output make a perfect new sealing surface for the new main seal (the seal can overtime wear a grove in the metal causing the leak)
speedy sleeve isn't neccessary tho. might wanna do the input retainer seal on the tranny. but againt not neccessary. on my bros former 85, the real oil retainer was actually what was leaking, not the main seal.
anyway, you gotta drop the transmission. Tranny jack helps but I've done it a bunch, alone, with just a floor jack and ratchet straps.
You'll need to pull the shifters (cover boot, shifters) you dont need to unbolt the covers, they pop out, the haynes manual might detail how they get out, but if you just look at em im sure you'll figure it out, they're harder to get back in than out, lol
the two 17mm bolts ontop of the bell housing are the hardest to get to, best way to get them out is long extensions (i mean like 2-3ft ) and a swivel socket to get up in there from underneath the truck. I have a 2" body lift and am able to get in through the shifter hole in the floor, without a swivel. but thats cuz of the body lift.
You can leave the cross member on, or take it off when you remove the tranny, I've done it both ways (on or off) and I prefer to leave it on even tho it can be in the way but its 4 less bolts i dont gotta touch and when you've done a few of these, you tend to get impatient
Once the trannys out, pull the clutch pressure plate, dont breathe in the dust! =), drop the clutch, you'll need a clutch alignment tool to reinstall the clutch so you'll want that before you go back to putting stuff together... they're a few bucks at a parts store .. cheap plastic thing
pull the fly wheel, you'll probably need to put a 19mm wrench on the front and some kind of bar to lock the motor from turning over when you break the flywheel bolts free... and same for when you torque them back down.
pull the oil retainer, pop out the old main seal, tap in the new one. Reinstall with new oil retainer seal, some RTV..
I'd reccomend draining the oil AFTER you do all this, so anything that falls into the pan will flush out..you dont need to drain it before you pull the rear.. oil isn't going to come spilling out, it pools lower than the top of the pan =)
Put it all back together.
hope that helps