IIRC, the twin 25-pdr mount was done to test if the chassis/turret could handle the recoil of a 17-pdr by firing both guns at once. I can only imagine how much of a nightmare the twin 25-pdrs would be to load in the event it entered service.
The Egyptian M4/AMX-13 hybrid and the Israeli M-50...
It's more pure fiction from Wargaming. Postwar in Australia, a lot of the turrets had been scrapped, as hulls were kept around for utility/farm tasks. So when the time came that people wanted to display the tanks, any turrets available would be used to make the vehicles look like "tanks".
The...
You would basically require a full-blown MBT to handle the 152mm XM150, and to my knowledge the only other tank it was even considered for was as a potential upgrade to the M60A2.
Honestly, while a lower velocity 105mm M68 or similar gun would work, a support gun would probably be best. It...
IIRC, the Italian 75/46 was comparable to the German 7.5cm PaK 40 in terms of performance. As for the original 75/34, I want to say it was comparable to things like the US 75mm M3. Although it's been ages since I looked into any of this.
Those didn't just stay as proposals, the 76mm M32, 105mm M68 (both with an without a muzzle brake), and a lower-velocity 105mm were all actually trialed on the M551.
Some of the images are old and woefully out of date, especially some of the original ones by David Bocquelet, but it's not easy to get them replaced, as oftentimes whole new illustrations are needed and the old ones can't be modified suitably.