The 1957 Model 6502 (Flat Face Cowl) units here in the US had a min GVW of 14,000 and max of 19,000 pounds. To get to the 19,000 pound GVW rating you would have had to upgrade to 10-leaf front springs, 13-leaf main/6-Aux rear springs and power steering.
The 1957 Model 6502H would have a 21,000 pound GVW, with 12-leaf front springs, 7000 pound front axle, 14-leaf main/6-Aux springs, 16,000 pound rear axle, V8 engine and 9-1/2" Hydrovac.
So, your front axle is 4,500 pounds and the rear is 15,000 pounds for a total of 19,500 pounds. I don't know why they rated you truck at 18,500, but it does falls under the max rating of the axles.
Mike B
