If the brakes were adjusted OK before they sat and locked up I would drive it about a half a mile before you decide to slack the adjustments. That should scrub the rust off the drum if that was the problem.
If the wheel turns free after a test drive then you should be fine.

Grigg

•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-