The O.P states that they have a 3100 truck with a 235 that has been sitting since 1997 and engine is free. I take that to mean that the engine rotates. As far as the carburetor, was the truck left at a standstill with gas in the carb? if so then it probably won't run without some work being done on the carb. If the other precautions are followed, I would dribble a little gas down the throat to see if it will fire.

1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy