During its production run, the M41 was also employed as a test bed for a number of different turret configurations and armaments including the 90mm M35 gun that was later employed with the M46A1/M47/M48 Patton series of tanks.
The M41/T49 variant was tested with the medium-pressure 90-mm T132E3 semi-smoothbore gun, which was designed to fit in the same space and weight profile as the original 76mm M32 gun, the same caliber but not the fully-rifled high-pressure 90mm M35. The new 90mm T132E3 cannon tested early APFSDS rounds. Trials started on May 5, 1954. The trials were a success, but the tank never saw mass production due to lack of interest from the military authorities. There was an artist concept of a M41 with a M35 but that was it.
T49 Light Tank with 90-mm T132E3 Semi-Smoothbore Gun
The T49 was an experimental variant of the M41 Walker Bulldog replacing the 76 mm armament with a 90 mm, identical caliber to the armaments on the Patton tanks (M46, M47, and M48).
That included the replacement of the 76mm gun with a 90mm, or in some cases a 105mm gun.
Taiwan replaced the original M32 with their manufactured variant of the M32 known as the M32K1. Taiwan also develop the T-65 which was their "improved" version of the M-41. They used the AAI 76 mm M464 APFSDS-T round for much better performance...
, which Denmark also used in their improved M-41DK variant.
In Brazil's M41B variant bored out the 76mm to 90mm for their low-medium pressure Ca 76/90 M32 BR1-3 guns which used the same 90 mm ammunition as the Cockerill 90 mm Mk III gun.
The 105mm experiment used the Cadillac-Gage Stingray light tank turret on the M41 Chassis. Never was adopted.
M41 Walker Bulldog with 105-mm L7 Low Recoil Force Rifled Gun
Reference: SHERIDAN - A History of the American Light Tank Volume 2. By R. P. Hunnicutt
BTW- The M10 Booker has gone into production for its intended role.
A correction: the newest variant of the M3 Stuart was the M5, with improved armor and frontal turret profile. The shortcomings of the Stuart usually involved using them outside of their intended role of supporting mechanized scout teams and flank protection. In one instance however, the M5s of the 2d Armored Division were pressed into service to breach the Siegfried Line! The ground in front of the German bunkers were so chewed up by artillery and the ground was so wet that it was impassable to medium tanks. The Stuarts zipped across under cover of smoke and took the bunkers under fire from the rear. This enabled other units to expand the breach. Also, IIRC, the 37mm had a very effective shotgun anti-personnel round.