Wasn't there also a variant that removed the turret in order to mount an 88mm in a casemate?
Not aware of any prototypes along those lines.
There was a prototype for a casemate assault gun on the cut-down tracked chassis of the AMX-50 MBT, using the 90mm SA47 DCA45 of the ARL-44 MBT (and a coaxial 20mm gun). Was abandoned in 1953, and followed by a number of projects for the "ELC" light combat vehicle instead until the early 60s, most of which looked like they rather belonged in the 80s visually.
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The EBR existed with:
a) FL-11 turret with 75mm SA49 gun ("short" barrel) for 1951 batch
b) FL-10 turret with 75mm SA50 gun ("long" barrel) for 1954 batch
c) FL-10 turret with 90mm D921 Mle F2 gun for 1963 upgrade
The relation of the SA49/SA50 to the 7,5cm KwK42 of the Panther was tenuous btw. What's known is that the engineers working on them did take a close look at it, and then probably sequentially switched out and redimensioned about every part until they got what they wanted.
The FL-10 was the AMX-13 turret, the FL-11 "the" EBR turret. Both were of the same oscillating design, but the FL-11 was a bit more bulky and could carry a heavier gun and an autoloader. Somewhat oddly in 1954 they started mixing and matching, building the next batch of AMX-13 with the FL-11 and the next batch of EBR with the FL-10 instead.
Between 1964 and 1966 all FL-11 turreted EBR were upgraded to the FL-10 with 90mm above, and all FL-10 with 75mm were scrapped. The D921 was a variable-pressure gun; the Mle F1 was the low-pressure version mounted on the AML, the Mle F3 the medium-pressure version for the AMX-13 upgraded at the same time.