Your wheelbase can change slightly with ride hight based on the rear trailing arm positions on the XX
Many, many years ago I knew of a class 5 car that might have been longer then the 105 inch WB the rules state. But if you lowered the front suspension to push the the front arms back more, you could get 105. At true ride it was closer to 107-108. Same with jacking up the rear, it would reduce the wb.
I was told Speeds arms did not lengthen the XX, it was still 95. The real race Speedcats RG built for Baja & Dakar were longer then stock. I think they were 105? Those were all real tubed chassis RG built.
Here's a good comparison of a stock XX and a 77" car. I believe it is currently bottoming out on the rear diff. If you are able to raise the rear diff, you could have additional travel without adding length. right?
That lower picture is not an XX. That's the "SpeedCat" that was was taken to Dakar and raced a few SCORE/BITD races. Full tube chassis built in house at RGM. The front of the chassis, and the back of the chassis are geometrically copied from the XX and the cab is extended. This car even had a turbo. I don't remember 100% but I'm fairly certain the wheel base was 110"
As for the 72" and 77" wide kits that SpeedSXS is making for the XX, those kits do not add to the wheelbase. That is for certain.