noting that H & H Fire Apparatus made the fire engine, and they are still around, try contacting them. The original photo is a mfr.'s photo and with the town/city/county available, they should be able to help track down the vehicle specs.
I have a 1933 Franklin with the same problems. Had the liquid drained and sent to a county hazardous waste site. Had the tank opened and sandblasted and then coated with a sealant. The removed metal was soldered back on.