What is the proceedure for replacing the 4 heater control levers in the dash of a 1971 280SL. Two levers control the temp, one controls incoming air and the last one controls the defrost/floor air diverter.

Is it necessary to remove the dash?

Thanks for the help!

I've done it twice
 

First time I removed the glove box and the speaker with its grille. Very difficult to access levers this way. The second time I removed the duct assembly and blower from below the dash and this made accessing the entire control assembly much easier. As I recall, guiding the control cables into their stays in the levers was the only tricky part upon reassembly.