First, the coupler post gets cut flush so that it protrudes about 3cm from the bottom of the frame. I then modified some coupler mounts I had from a MTH car. They get cut in a plus design flush to the hole so they'll sit flat on the Aristo posts with the posts stiffners locking into them. The bottoms of these pieces gets a notch so that they will fit around the rear pilot piece as they're screw mounts won't work. Hopefully the pictures will help clear up the descriptions.
The MTH electro-coupler doesn't get touched this way and their return springs will keep them straight.
One other thing that needs cutting is the pilot above the coupler so that there's clearance for the taller electro-coupler. After mounting, I used hot melt glue to help reinforce the assembly. Make sure not to bond to the coupler itself.
This is my first blog, so bare with me.