Howdy
I found some info in an old copy of AFV Weapons Profiles 26
small quote on the T49.
A memo to the General Staff Dated December 2, 1941 recommended that a 37mm Gun Motor Carriage with a Christie type suspension be developed. At the time a Tank Destroyer was defined as differing from a tank in having thinner armor, greater speed and an open turret. Such a vehicle was lighter, had greater crew vision, but gave less protection.
On April 1, 1941, Ordnance convinced G3 that the 57mm M1 gun should be used in place of the 37mm gun planned. An agreement was made to make to prototypes for testing.
the T49 Gun Motor Carriage was to be highly mobile, weight about 12 tons and have a crew of 5, and be able to reach 50 mph in speed. Armor was to be 7/8 inch on the turret, hull front and sides, and top and bottom to be 3/8 of an inch thick.
After a test of the first prototype the Ordnance department agreed to develop the 2nd prototype with the 75 mm M3 gun from the sherman tank and it was to be known as the T67.
and thats all all the info about it in that.. the photo they show is the 2nd one you posted.
also found this photo.
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Delbert