Just to confirm that SLR was spring in the levers and improved lined cabling. So the SLR position in the canti is for these levers. Use the other position if you levers do not have the return spring or if your cabling is poor
It can also be used if your springs are well used and just not doing their job in SLR setting.
Under bars are Rapid fire+
I personally didn't like the XT/XTR at that time, the cheaper LX and below had better paddles really.
I went to Gripshift and didn't look back. I do now use some much later XT 750 from this century. Even 737/739 levers while they work better have a horrible feel.
But if you want to go for some. Get STX-RC/Alivio on their own versions. Work well, fell fine and streets ahead of the early 90's shifters. Then get some nice brake levers.
you'll find plenty of the old instruction manuals in the archive on this site. Including the SLR brake setup if I remember correctly