I decided to make the new mag length at 2.600", and scored a line on the top plate to cut back to.
Remove top plate back to line with dremel, and remove rear wall flush to interior magazine sides. A file and chisel will help trim and smooth inside the magazine. Use an exacto knife to square the corners of the cut and back bevel the feed lips on the magazine.
Te new rear wall will be a piece of aluminum channel used to trim edges of 3/8" plywood. Cut at 1.620" inches.
Net thickness is a little less than the ID of the magazine, but some 10 mil tape on each side will make a nice fit.
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