I would doubt that it has any of the three higher nickel content gear sets. Early Cobras used Ford passenger car transmissions like a Galaxie with one of the small V8 engines. Like many Ford subjects T10s by application is complicated because over all lengths, pilot lengths, and where shift mechanisms mounted varied by engine type and type of vehicle. Shelby American registered several different standard and optional gear sets for the cast iron cases Galaxie small block configuration assemblies with racing organizations.
The various ‘high nickel’ gear sets didn’t get to Cobras in production until the change to aluminum main and tail shaft cases.
Cobra wise, all other Ford and General Motors (GM) (K set) cars excluded:
B set = standard passenger car gears, also used in Cobras 1962-63.
XCO-270 transmission set, origin unknown at this time. Cobra race.
J set = standard passenger car gears metallurgically, may or may not have gotten into new street Cobras.
K (high nickel) set = installed into aluminum cased Cobra transmissions, street and race, introduced sometime in the CSX22xx range it is believed, example CSX2246 had a K set originally, my black car CSX2310 was fitted with a K set. (The K gear ratios originated in some high performance GM cars.) Listed as the alternate gear set in the February 1964 Cobra reconfirmation of registration for roadsters and coupes with the Fédération Internationale de l'Automobile (FIA) race sanctioning organization.
L (high nickel) set = installed into aluminum cased Cobra transmissions, street and race. Listed as the standard gear set in the February 1964 Cobra reconfirmation of registration for roadsters and coupes with the Fédération Internationale de l'Automobile (FIA) race sanctioning organization.
M (high nickel) set = introduced into aluminum cased Cobra transmissions, race and street, introduced sometime in the CSX23xx (CSX2321 has M gears) range it is believed, it is believed that the later the chassis was the more likely it was fitted with a M set. Legends says they were called “Sebring” gears because SAI first used them in their race cars at the 1964 Sebring race. The Feb. 6, 1964 reconfirmation of what was submitted to the FIA (with pictures of CSX2138 and the first Daytona Coupe included) shows L gear ratios standard and K ratios as an alternative. The M ratios are not listed at all on that document. SAI was into finishing late CSX22xx and early CSX23xx chassis at the time. My black car (CSX2310, end of March 1964) came with a K set.
The tough part to deal with is that chassis were not finished in order so it is meaningless to think that since car CSX2xxx was fitted with "such and such" that chassis CSX2xxx±1 or 2 or x received the same part or assembly. Early made parts and or assemblies can be in most any car but late made parts or assemblies cannot.