Don't get discouraged, we'll help you figure it out. Sometimes we may need to work your camera pretty hard to get it done.
If you have six lug wheels, which I believe you confirmed up above, you have a 1/2-ton. Or at least the significant parts of the drivetrain are all 1/2-ton even if other parts didn't start out on a 1/2-ton.
Six lug wheels equal a half ton on that era of truck. No other GM truck has the six lug wheels.
Eight lug wheels could be either a 3/4- or 1-ton. You don't have eight lug wheels so you have a 1/2-ton.
Given the open driveline you can not assume any of the drivetrain is stock. The rear axle and possibly more is later stuff.
The best way to know your axle ratio is to open the differential and count the teeth. The easiest way is to first put blocks in front and behind both front wheels, then jack up just one rear wheel and count how many times the driveshaft turns for each turn of the lifted wheel. Then do a little math.
Can I put math in a sentence? (number of drive shaft revolutions) divided by (number of tire revolutions) times 2 would give the approximate gear ratio. If you have 4.11 gears expect to see the drive shaft turn just more than twice for each turn of the wheel.
If your gears are 3.90 you'll see just less than two turns of the drive shaft for each turn of the wheel.
4.57 gears would mean two and a quarter turns of the drive shaft, so you do need to watch pretty carefully, because you'll want to see the difference between 2.05 turns and 2.28 turns. Not hard to discern if you are watching.
Most of us are here because we want to share what we know with others, so we'll enjoy helping you sort this out.
