Here is the update I should have posted weeks ago.
I thought I'd ordered a flange with pipe ID to fit over the original pipe's OD, but instead I got pipes the same OD.
So that meant a butting-splice {or welding}, using the 3" wide clamps I mentioned before. We used a portaband saw to cut off the rusted 1+" of the front pipe.
The flange I got matched the bolt holes on the existing replacement muffler. (That was wider than the front-pipe's; the bolts had been canted out 30 degrees.) We shortened the replacement flange pipe to fit, then used the 2" dia Autozone clamp. What we actually needed was a 1&7/8" diameter but did not find such. So we built up the front pipe with a 1.5" wide piece of of furnace duct sheet metal wrapped around it.
We gooked up everything under the clamp with muffler sealant, cranked down on the clamp''s bolts to ~80 ft-lb and let it set for hours.
Thus far, all is well.
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