21 years ago I was in Germany and went by Lothar Stockl's place 914 + 911 KFZ Teile Versand GmbH in Bempflingen, he had replacement shells for 914-4 heat exchangers. Initially I didn't think this was a good idea, but if the exhaust pipes are not pitted or rusty. It's probably a reasonable solution, plus the fact that I've never had problems with exhaust flange leaks with factory heater boxes

I haven't been able to find a website for Lothar. Has anyone used the replacement heater shells?