Unfortunately, ma Mopar didn't see fit to keep track of how many cars were built in a certain color. In 1971 there were 10,098 demon 340's sold. Haven't been able to find a break down on auto vs 4 speed either. I wouldn't be surprised if less than half were 4 speeds.
EL5 is actually a Plymouth color, and I've been told that it had to be ordered to get it on a Dodge. It was actually considered one of the "high impact" colors. I would imagine that combo would be fairly rare, but I don't think you're going to prove it was a "1 of ..." car. I have seen a few Demons in that color, although I have no idea if they were 340 or 4 speed cars.