I removed the cell from the Edmund 4" and pulled out the glass. I repositioned one of the spacers that had moved and got the Newton's rings close to centered. Cleaned the front and rear surfaces, where the haze was, and partially cleaned surfaces 2 and 3 to remove glue left behind from the migrating spacers. There were three tiny spots of fungus on the front surface that wouldn't come off with alcohol, so I resorted to bleach bathroom cleaner on a Q-tip, which took them off completely, and then cleaned the whole surface again.
Then I cleaned the rust from the retaining ring and sanded out a couple of rough spots on its threads, and cleaned the cell itself. Also worked on trying to get the purple stain out of the tube paint. The only thing that touched it was isopropyl alcohol. It reduced the intensity by about half, but that was a far as it went. One thing I tried actually left a yellow stain, so I spent time trying to remove that and finally found that Flitz would take it out. It's at the point where you'd only notice it in good light.
I put the cell back onto the tube, adding some toothed lock washers under the screw heads to make it easier to loosen and tighten the acorn nuts for collimating the cell. Then I put the glass on the floor (on a tissue, on a piece of poly foam) and lowered the tube/cell onto it. Picked the whole thing up and turned it upright, and lightly clamped it in my bench vise and put the ring in. But then I realized that the rear element was now coated in dust. So I unloaded the glass again, and cleaned it, as well as some smudges between the elements. Then got it back in the cell.
There's a fluorescent bulb over my workbench, so I checked the Newton's rings again, and they were way off center. So then I spent about an hour fussing with the spacers and cleaning glue residue off. The rings eventually got to within about half an inch of center. There are still some places that could use cleaning, but it was late and now that I've had five rounds of loading and unloading the glass, I'm not as worried about going back in. Eventually it may be necessary to replace the spacers.
Then I put the whole tube face down on some black felt and used a Cheshire to collimate the cell. It's a challenge to get above the peephole of such long scope, and then hold the tube steady while bending down to tighten the acorn nuts. Had to back off and try a few times, but finally got it locked in with the blue and yellow reflections aligned. They aren't quite centered, so I'll have to work on collimating the focuser next.
I replaced the corroded nuts on the 1/4-20 mounting studs with stainless and found that they fit through a Losmandy plate, so I put it on that with some wing nuts, then loaded it onto the 706 mount and got the RA axis balanced. The protruding studs don't allow enough backward movement to get the Dec axis balanced, so I still need to make standoff brackets to get more flexible positioning. But at least it's now usable, in case I don't find more time to work on it before I take it to an observing night at school. Hopefully we'll get some clearing tomorrow night, so I can star test it.