Correct, the "nut" is a rectangular bar with tapped holes for both bolts.
Some penetrating oil and lots of torque is you best bet. Even if you break off a bolt or two you'll be OK in the end, they and the nut plate can be replaced. If it comes to it, with the nut plate out you can probably remove the broken bolts.

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-