Can't tell by looking at your pictures which is which, as far as fit. Like FJ5 Fish said there not right for a E body, why pay big bucks, if they cost a lot?

I believe these are the 2 filler necks for challengers. The one on the left is for a 71 with N95 and like FJ5 Fish said for 70 N95 cars.
Look at yours and see which one you have. The one on the right is used in 1970 without N95 72 73 74.

Then these two after markets fit challengers filler necks and also I beleive some 68 B bodys too?
The one on the right is for the filler necks on the left in the above picture.
See the difference in the distance between the locking tags and the rubber gasket? That's what you have to lookout for.
These caps can be had from Car Quest and other parts places for around 15 bucks , so be warned. Don't have to pay huge prices for a correct funtioning but wrong cap.

This is what they look like installed.

Here's a original one.