Anyone familiar with the process of changing the heater core on a 75 roadster with factory air? Does it require the engine firewall plenum to be pulled or is is accessible from the interior? If so, I assume the top dash pad needs to come off and the passenger side dash face needs to come out. Does all the air distribution ductwork need to come out also?
Any insight is greatly appreciated!

 

It's been soo long since I did mine I can't recall if the firewall plenum needed to be removed for just the heater core but I recalled I had to replace all the gaskets and seals on both the A/C plenum and the interior ductwork. The seals on both sides of the firewall were all deteriorated and plenty of hot engine compartment air was flowing into the passenger side of firewall. I expect on a '75 car if it hasn't been done it needs to be done. I didn't seal up the A/C plenum with the monkey poop stuff like stock but instead just used RTV - much easier to work with and should last just as long. Something else to note I shopped most the auto parts stores for a replacement heater core but none were an exact match/fit - the tubing needed a little bendology but it finally fit.

Good luck.