The sad news is my nearby sources are out of 17/32 brass, the good news is I worked out a fairly easy way to do the AR removal sans power tools.

Step 1: invest in a $10 basic pipe/tube cutter. Cutting right on the seam works, but having done it, I'd advise about an eighth of an inch further towards the end (hit the middle of the AR chamber rather than right near the post support).

Step 2: Find some 7/16" brass tube (1/2" might work, but is probably too large).

Step 3: Wrap the end of the tube as neatly as possible in E-tape until it makes a clean friction-fit in the back end of the formerly-AR chamber. Use your tube cutter to liberate about half an inch of wrapped tube to use as an insert.

Step 4: Fit the pieces of the plunger back together around the tube segment (you may need to shave off a little of your E-tape to get a good fit, you want the seam to be as narrow as possible) and carefully hot-glue all the way around, working the glue as deep as possible into the seam. If you haven't wiped most of the original oil off by now, that may be necessary here. Once the glue cools, use a sharp razor to shave the glue down nearly flush with the plunger. You have a little bit of leeway, and leaving a thin layer of glue probably helps make a good seal when you reassemble anyway.
I also found a couple more Eliminator specifics to watch for:

The orange cap the barrel fits into is all kinds of asymmetric. The top and bottom flanges are wider to one side than the other. The wide side fits into the screw-receiving half of the shell. There's a notch on the barrel-receptacle that fits a post on the barrel, which should also face towards the screw-receiving half of the shell. If the front of your gun isn't closing properly, check the orientation of the cap before forcing it.

There's also a tiny little sight piece that fits in between the halves of the top grip. It is also asymmetric, and only fits one way, but is easy to figure out provided you don't lose it.
So, pending finding the right tube for the barrel, I at least have an Eliminator that survived being forcibly opened and cut on the AR seam, which fires about as well as reported on the IX-1 and still looks fairly good. All tools and materials used (save for a bottle of SAE 20 3-in-one oil for re-lubing) are present for the photo, and as scale reference.
