I searched the forum, and the faq, and did not come up with a clear answer.
Can I swap just the LSD from a 84-85 GSL/GSL-SE into the 84 GS?

What else is needed to go to a disc brake setup later? (Can I use GS axles, trailing arms?)

Reason why I ask is because it is fairly hard to find a complete rearend or parts car locally, and shipping would be pretty pricey for the whole rearend.

Thanks for your help, and please don't tell me to search, I spent the last 15 minutes reading posts with no definite answer for what I want to do.

 

All 84/85 axles have the same diameter/spline count and pinion length/driveshaft flange size so yes you can just put the whole third member from a GSL or GSL-SE into your S/GS housing and it will work fine.

If you later want to get disk brakes as well then you need to get the disk brake axle housing (GSL and GSL-SE housings are exactly the same, it's just the axles that differ) as well as the brake backing plates to match. At one point I think Re-speed was talking about making a kit that allowed you to put disk brakes onto a drum rear housing, but I don't know if anything ever became of that.

Just to add a bit more info, if you were planning to re use your diff carrier and install just the LSD unit itself then you can also widen your search to the NA FC's (86-88 GXL and 88 GTU to be specific) as well as the 1.8 liter Miata as they will all fit a FB ring and pinion and housing.

In all cases, the 81-83 GSL diffs are of no use to you as the axles are smaller.