I need to fabricate a heater cable due to running Tangerine Racing heat exchanger.

Does anyone know what gauge of wire the cable is and is there a certain type of steel wire that I should be looking for?

If you want to replace the cable, you should use music wire, around .045-.050" dia. However if your original cable is in usable condition it's within a couple inches I think, to reach the new position of the flappers.
I was taught a simple method to extend a too short flapper wire is to add a long small diameter cotter pin as an extension, with the cable secured around the loop of the pin.

I have a small roll of .051" music wire here. I'd be happy to send a suitable length to you to make a new cable.

Thanks Chris

I'll get back to you once I know what length I need. I'll do some digging to see if I can find my old cable and see how close it is

Original cables are still available from Porsche. Pricey, but are correct stiffness, are plastic coated to glide better in the tube, and have terminals crimped on for a solid fit in the barrel connectors on the flappers.

914Rubber has them as well