Will it start? 1978 GMC 3/4 ton 4X4

We drug this 1978 GMC out of a cow pasture in East Tennessee. I wanted the axles out of it because it was a 3/4 ton 4X4. It was parked over 20 years ago, and I have no idea why. The engine had been rebuilt at some point, but I don’t know when. After we got it started, we put 5 gal of gas in it, and it Ran like a top. The fuel gage read full even though it had no gas it it before. I speculate that’s why this truck was parked. “It ain’t got no gas in it!”