The steering wheel column can be lowered and removed after you have removed:
1. The rag joint in the engine compartment.
2. The two nuts and bolts at the firewall.
3. The two nuts under the dash gages.
4. Electrical connections.
Yes, your upper dash pad looks beat, but the stuff below still looks pretty good.
I replaced my heater core in my '73 with A/C, and it didn't have anything to do with the A/C Evaporator. I also used a hand operated vacuum pump(Mity-Vac) to check all the heater controls and found two leakers. The whole heater assembly looks complicated, but once you get it off and on the bench, it all makes sense. Take lots of digital photos before disassembly!
John
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1973 BB 4-Speed Coupe Project Car
2009 Z06 Mostly Stock