Newbie needs help, please.
What is involved in converting a GS rear axle (drums) to GSL rear discs? (GSL, not GSL-SE)
Are the axle setups all the same?
So an LSD will fit inside the GS open diff housing? Axles mate up?
There's a sordid tale behind all this. Thanks for any help!

The center pumpkin of any 84-85 rear dif will interchange including the GSL-SE so that would get you an LSD but no rear disks.

To convert from drums to disk is more involved. You would have to swap the entire rear, rear parking brake cables, and brake proportioning valve. Bolting the rear is easy because the mounting points are the same. The reason you can't just put disks on a GS rear is because the axle housings are different. The drum rear has 4 bolts on the end and the disk has 3. ReSpeed does sell a 3 bolt end plate to convert a drum housing to disk but it requires cutting off the end plates and welding on new ones. I wouldn't recommend doing that unless you are a great welder.

Thank you, Chris. Very helpful!