I have a 58 3100 and I am having a heck of a time finding the right heater core. My truck did not have a core inside the heater box so I have noting to go by. I have bought 2 cores from sellers( on Craigslist) claiming to sell parts from 55- 59 2nd series trucks and neither of them fit. They are both way too large and the inlet and outlet do not line up with the cut out on the firewall. Does anyone have the exact measurement( length,width and depth) for the deluxe rectangular heater core. I have looked at the pictures posted by red here on the forum but at this point I need to know exactly what I am buying from future sellers .