[57chevyman]

my idea about rigging a different core that fits in the box is to either
1. find one that has the inlet and outlet 4 1/8" apart, or

2. mount any old core in there and attach bulkhead fittings to the firewall, and just plumb that to the core with short sections of heater hose...

but hooking up the control cable to a generic valve somewhere could be tricky. probably easier to do that on the engine side of the firewall