At that time 18 had a 1954 Mack "L" model, 1000 gallon pumper. Pretty sure it was "L".
Photo of E18 with their next rig on this pageI was looking at John Calderone's book and the year before the fire alot of companies got Mack C model pumpers. As you said not E18 though. Could their next new pumper have been a Mack CF? That would mean they had the '54 a couple more years into the late '60s. I'm no expert but I think the first CF models were in '69.