In the serial number H540015240, the H designates the 3100 series (1/2-ton). The 54 is, of course, the model year. The letter after the 54 designates the manufacturing plant. What you had typed as a number 0 (zero) I assumed is really an O (letter oh), which stands for Oakland, CA.
Did you ever determine anything from the engine casting and/or serial numbers?
