The ROTJ Shuttle was a little smaller than 1/72 scale, perhaps closer to HO scale which I believe is 1/87. I have one next to my desk.
The original ESB AT-AT, on the other hand, came with several miniature snow speeders in the same scale as the AT-AT (don't know if the snow speeders made it into the ROTJ issue). These things are tiny, about the size of your thumbnail. I'd guess they are a similar scale to the 1/350 scale planes that come with aircraft carrier models.
I guess it would be kind of like trying to display a 1/72 scale jet on top of your 1/350 scale aircraft carrier.