I’m not familiar with this engine. I looked at the parts breakdown on Lionel’s site. A shorter coupler doesn’t look like an option. You could get some aluminum or brass stock the width of the stock coupler mount. Use the stock bracket as a guide to drill out the 2 holes. Then mount the Kadee to the bracket. The do offer a shorter coupler box than the standard 805. This would still give a coupler that moves with the truck. As long as these 2 are always coupled together. I wouldn’t be concerned with getting the coupler at the proper height.
I did this years ago to a MTH DL109. Looks much better now.