Need pics to confirm........but from your description you have an Qlympic arms upper.....does it have a spring wire ejector pinned into the UPPER about 2/3's of the way back on the ejection port. Is the bolt two piece (carrier & bolt) and uses a standard AR firing pin....not the usual 9mm pin. If so it is Olympic. Will it fit on a current Olympic lower.....you'll just have to try. I have a 40 olympic barrel and bolt......and it came from a gun that for some reason would OOB about every third round..... it was most unpleasant to shoot.
If the mag are single feed than they are probably converted 41AE or 45 acp  uzi mags and if the "cage " as you describe it is CAREFULLY removed, they can be used in an UZI again.

Rock River had some stick 40 mags....I have a few on the shelf I played with a while back.....they had reliability issues , wish they had contacted me......they put the mag catch slot in a place where the mags sit too high trying to make it feed when all along the isssue was in the bolt abnd barrel. wish they ask, for a consulting fee, I'd be happy to show them what was wrong