Its Not A Posi

A local guy has a 71 Challenger and whenever he shows it he is quick to point out that it is one of only 465 produced and it's still got the original 383, Muncie 4speed and a 4:11 posi rear end. I have explained to him several times that he has a New Process A-833 transmission and the rear differential is called a 4:10 sure grip. Yet, every summer he tells as many people as will listen that he has a Muncie and posi.
He wants me to work on it occasionally and I replaced a leaky fuel pump one time and put on some correct plug wires another time. He wants to hang around while I work and blah, blah, blah about how wonderful he and his car are so I politely decline. Plus, his posi drips on my shop floor!