Back in 2005 when I did my 71 E body, I could not find the correct size 3 pin switch for a E body. Like you said I remember finding one but it was the wrong size thread. Wonder if it was for a B body since I think it was too big?

What I did at the time and it still works fine today is build one out of I think was 3 switches I bought. Each switch had part of what I needed. Can't "cut" the wires on a 3 wire 71 door switch.

I read here that they are available on E bay and other places now, but I am not sure.