Can you add pictures of the RNS-E. it should only need cutting to the size of the A2 opening.
If you can add an image from the rear, close up but showing everything as you’re looking at the back I will be able to draw on the image to show you what is needed to be cut away.
Dremel, fine file and some 120 grit wet and dry and it’ll look likes it’s always been in the A2