As stated above, they are different size. There is a solution I have used twice to accommodate the longer length. Go to the hardware store and purchase a pair interlocking flush mount cabinet hangers. Cut a piece of plywood to the needed width and length to accommodate the mattress plus about 8" to cantilever the extension. Use the hangers to attach the extension. When not in use store the extension under the mattress. You should have enough give in the mattress to pull in the slide. If you are really tight, let the air out of the mattress.
2016 Winnebago Journey 40R - 2012 Jeep Rubicon
2 Arctic Cats, 3 Shelties, 4 cats
Bottle of Jack Daniels & wife