Putting in "davesclassiccars.com" in my browser comes up with "this website is for sale" for an outrageous sum, although there is a "Dave's Classic Cars" that appears to be a legitimate dealer near Springfield, IL. Link No 54 trucks listed there currently.

The 1954 Vehicle Information Kit indicates that there's no frame serial number, just body, engine, transmission, and rear axle. The only serial number that starts with H54 would be the data plate on the dooor pillar.
You could point him to the GM Heritage Center Archive so he can see that information for himself.

I recall seeing on here that frame serial numbers were used on later year trucks.

Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.