I wasn't completely satisfied with the way the main engines mounted. The side of the engine had a square hole that mounted on a square peg on the Mule. I was worried that they would fall off if I moved the replica. Here is my solution:
I made a template that fit into the mounting hole on the engine and drilled two 3/16" holes.
I inserted refrigerator magnets into the holes drilled into the engine. I thought I was going to need some epoxy but it was a nice snug fit.
Using the same template, I transferred the hole pattern to the square mount on the Mule and inserted a second set of magnets.
And then "SNAP"! A nice strong mount. It actually takes a little bit of downward twist to get the engine off for future storage. Now to repeat the process for the L/H engine.