i took the heater box out of the 57 3100 truck to do a restore on it and my heater core in it one of the outlets is damaged and the core needs to be replaced but from what i can see and tell the heater core is round and i have looked in all of the truck books tht i can think of and im not seeing access to a replacement is there no where to get a repro new round heater core??? in a 57 3100 tuck its a standard heater by the way.