im of no help with the location, id just say that the resistor you are looking for, for the heater fan is likely not far from the fan wiring, if it exists. since the resistor creates heat it might be located where the heat can be dissipated. the green multi section wirewound resistor looks just like the one volvo used in the heater fan arrangement, but was updated with a different switch and different motor, eliminating the resistor in the "upgrade" .. If the blower motor quit, people would normally change both the switch and the motor, and then there would be no resistor , to find.
if you can go here, it shows the old and the new "system" side by side. That's Volvo but maybe porche did similar, I don't know if that is the case.
https://www.ipdusa.com/products/22228/Blower-Motor-Update-Kit-140-200-73-93-Aftermarket-Volvo-1323849-1370240-9131943
I did just find this video, by Pelican showing the resistor location.. , maybe that solves it?
watch this :
https://www.youtube.com/watch?v=rplsRvJ5mR4&ab_channel=PelicanParts