This is a Pre-Ban, Eagle Arms "Action Master".

The Flattop is apparently NOT milspec, because when I try to mount USO Posi-shift, and other GI products on it, it's loose.  Shaky, actualy.

What do I need to do, so that I may mount some of these items?

...would a GG&G F.I.R.E. rail do it?
Or an ARMS #38?

My guess is that no, it wont work. The GG&G and ARMS rails both use and are made to mount on mil-spec 1913 rails. If other mil-spec mounts are not fitting on your flat top, I dount the sleeves you mention will either.

Only solution I can think of is getting a new flat top upper. If it is an Eagle, I would try to contact Armalite/Eagle and see if they will do it for you. You might have to put out the money for the upper, but they may do all the work for free.

If they dont, if you buy a new flat top from Bushmaster, I think they will swap them out and reassemble you upper for free.

Just some suggestions.

My GG&G Offset mount fits fine.

Throw lever mounts are loose.

US Optics Posi-Shift is loose.

I don't want to get a new upper, because it's a match rifle.  The fit between the upper and lower is super TIGHT.

I think that the Arms #38 sleeve would be the best bet to convert to the real milspec, then the throw levers would also work.
Good Shootin, Jack