Please give a specific model. The dump bodies and hydraulic system will be aftermarket, but you there's no way to tell you anything if we don't know whether you're talking about a 1/2 ton C/K pickup or one of the Class 8 trucks Chevrolet manufactured at the time (Chevrolet exited that market in 1980; GMC followed suit when their heavy truck division was bought out by A.B. Volvo in 1988).
13000
2,000 pounds
A tandem axle (ten wheel) dump truck can typically weigh between 20,000 and 25,000 lbs., depending on make, model, steel or aluminum dump body, etc.
I found out how much my truck was by going to the dump, your recipt will have your before and after weight. A truck stop, Hwy weigh station or salvage yard also have scales and could give you an exact weight.
I own one with a 5 yard dump box on it. I weigh in at 11060lbs empty.
One version of the 1974 477 (gas) dump weighs about 13,600 lbs. (6169 kg). (compared to a 1972 F600 with a 359 HD dump, an old Weirton Steel workhorse, at 9980 lb or 4527 kg)
it weights 2330459556 lbs
Interstate weigh stations require any large truck to stop at the stations when they are open and active. A dump truck qualifies as a large truck that would need to stop.
15000 lbs.
In the vicinity of 22,000 - 25,000 lbs.
None without fabrication.
Not sure, but I hear they are pressed on!