If I am pulling the axles and putting them back in the same rear end, if I don't mess with the back lash adjustment, do I need to check anything?

what happens if it is off?

8 3/4 with a 742 one-legger.

You check the axle side play (in and out total movement on both sides before removing them and install them to or real close( .001 to no more than .003 differences ) what it had originally
This applies if your working on a 1965 and later 8 3/4 with the conventional axle ends and the end play adjuster from the factory, if it is pre 1965 you will still need to end up with the same side play readings but it has to be done with shims, no adjusters from the factory on them
I think the FSM call for no more than .008 end play total at room temps. with every thing cool , not warmed up by driving

ah, so it is more like bearing preload.
Thanks.

That's exactly what it is.

Not preload but free-play. Preload, like on the pinion and carrier bearings, applies constant load on the bearings while free-play allows the axles to move a little.

I bring this back up because I finally got to pull the axles on this.
I remember the adjust lock and the thing to turn on my 68 fury with the suregrip.

This one didn't have anything to turn, and no lock.
do 1 leggers not have an adjustment?
Did I miss it?
the passenger side did have a teeth type thing but there wasn't anything threaded under it. It just spun free, when I went to clean it, and didn't spin at all once the axle was bolted in.

This link should explain everything you need to know.

8 3/4 Adjustment

odd that piece especailly the lock tab is missing. I don't think it has ever been apart.

what part(s) are missing exactly? Just the flat lock tab with the "tang". When resolved, adj it to .010" end play. I like to go in solid then come back out to .010". Why were the axles pulled?

I think the adjuster, or whatever makes it take up space is missing and the lock tab.
how does the adjuster work? that is what unscrews to take up space?

I pulled the axles, to remove the drums and backing plates, and I replaced them with the tsm disc conversion kit.
I never saw a locking tab.
That area was gunked up with what I guess must have been caked up grease and some diff fluid.
I blew it all out with brake cleaner and then repacked the bearings with grease.

I think the adjustment plate is there, because it had the most crude caught in it. I had to use one of those straw attachments to clean all the stuff out of it.
It does not turn freely once I bolted the axle in.
But I didn't see any threaded parts under it.

If there is no adjuster, somebody might have replaced the original axle bearings with the Green ball bearings. Some pics would help.

sorry, all back in the car.
that does look like the piece I had to clean the gunk out of.

I guess based on your pic that is threaded into the part that holds the axle on.
if so, it is locked up tight and doesn't move anymore.