Light engine probably refers to your gas v8, as opposed to a diesel. If there’s a center circle sticking through your rear wheels, that’s a full floater rear end. The caps unbolt and that’s how the axle shafts are removed. A semi float fits flush inside the wheel.
You can have heavy duty suspension with a light duty engine, btw. You’ll be able to carry weight, you just won’t have much power for acceleration and hill climbing.
Whatever you find, just don’t max out you weight. You want to leave a cushion for you, passengers, cargo and fluids (gas, water storage). A vehicle loaded at 50% of it’s rating is going to handle differently/ better than one always at it’s upper limit. It will use less gas as well. On a positive note, with a little weight in the back, your truck will ride a bit smoother.