Probably just the clutch is stuck from sitting, rusted to the flywheel.

Pull it out of the shed and try starting it in gear with the clutch depressed and the brake on, it might break free and if so that was simple/quick. If not put it in high gear (not running) and rock the truck forward and back with the clutch depressed.

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-