This is the CATTB, which was pretty much a project to put as much new stuff in the M1 as physically possible. The Thumper was meant to test the 140 XM291. They are somewhat similar, but also very different.
Are you sure?
From what i can find, the idea was for the german one to have an autoloader, it was part of the original design however it was never implemented when they attached the turret to the hull
Yep.
The autoloader needed a redesigned turret rear. Was made by wegman and co.
It was actualy a 2AV turret (T19) modified with the autoloader.
First mounted with a 105 on a leo 1 then with the 140 on leo 2.