hey guys, got one more for you, i got a hole in the heater core in my GMC 77 k15 and i need to replace it. all the instruction books say to remove the "stud bolts" that hold the heat distributer to the fire wall. there are three of them but they are flat bolt heads with no hex head or screw driver slots, just flat. looks like large nail heads sticking out of the firewall. the books say they can be removed from inside the cab but i cant see how. the engine bay side of the fire wall is covered by the a/c blower unit. do i really have to disassemble the a/c? thanks, sawbones.