Slot the firewall cable hole, and increase the size of the large hole in the inner firewall, until straight line access to the demister/interior direction lever on the heater box is achieved.

Add a cable clearance hole to the panel between the console and bulkhead.

Swap the heater/demister controls left to right and rotate through 90 degrees such that the Off positions are horizontal. Demister assembly should now be horizontal. Heater assembly vertical. Both cables now make a smooth transition from the firewall to the controls.

Attach the heat cable to its console switch on the bench while swapping the controls left to right to permit access to the cable clamp and trunion tightening bolts.

Demister/interior cable can be attached to console switch assembly with access through either the radio aperture (or from above before the I/P is fitted) to secure the cable clamp and trunion.

Fit the console to the car while passing the heater cable forward into the engine bay for connection to the heater tap later on.

Finished result.

Note 1: It needs to be understood that the heater/demister cable length must be finalized early on. Fit and refit cable as required to align and establish inner and outer lengths. Initially attach a longer heater / demister cable to the heater box flap lever. The outer cable can then be removed and re-fitted as often as is required to establish cable length by guiding it in and back out along the inner cable.

Note 2: The demister tubes are my own improvisation, originally from an old vacuum cleaner!