Actually, there shouldn't be any
The fitting should be so good that they are unecessary but things are not that way for lots of reasons.
I assume that you have these abominations to correct deficiences and cost cutting.Might I now refer you back to Pete Boas excellent notes on your problems with saddle corrections etc?
However, a bit of a lecture - or more?( You CAN delete it all) Pete advised you to change your gibs and alter the adjusting gib screws to bear on the dimples( there may not be even those

) on the gibs.
Now I am telling you to change your top slide gibs from 'bits of rectangular steel' to something which does not rock about like a pea on a drum or FitzHenry- FitzHerbert! GHT saw these problems and recomended that the Myford ones- which were a little better than rectangular strips were pinned, had rounded gib screw ends and had- something to pin the whole lot to fasten down each cut.
If you go to Ian Bradley- on the Myford, you will find that his solution was to add more gib screws!
Tonight, I'm sitting looking at my 'before Myford' vertical slide and I note that it has all these modifications.
Sad to relate, you are not alone. I've got a little Unimat 'clone'- a MJ189 and if I am going to keep it, I am going to replace the 'airgaps' in more than just the top slide.
Am I wrong? Well, my gibs in the cross slide on my Myford have rounded screws but the gibs are adjusted to work in two directions- at 90 degrees to one another- and are in two sections.
Well, now? Lots to do on a snowy weekend, eh?
Regards
Norman