The R107 roadster series . . . those would be the 450SL, 380SL and 560SL here
Some smarty pants is probably about to point out that there were other roadsters in that series, but they weren’t sold here in the USA. Any 300SL with the 103 engine . . . to cite just one example of the others . . . registered here in the USA is a gray market car and didn’t arrive through regular channels
And yes, it did seem the heater core and evaporator were built around the car. The book time to replace them was staggering.