Narrow pattern aluminum case was Cobra , lite weight Galaxie, Thunderbolt only. GT350s had the wide flange and short tailshaft in aluminum.
Then you consider gear sets. There were at least three different gear sets for aluminum transmissions in Cobras. Not every set has the same desirability.
Here is what is listed as SERVICE transmissions and one race part as of May 31, 1965. (direct quotes from Shelby American parts book)
C3AZ 7003- H Transmission, 4-Speed Stock Cobra Steel Borg/W Ford Ea 320.90 258.32
S1CS 7004 Transmission, 4-Speed Stock Cobra Aluminum AS2T/O-L Warner Gear Ea 323.13 258.50
S1CR 7005 Transmission, Pontiac Racing Gear 93, SK4516 AV Ford B/W Ea 319.80 223.86
S1CR 7006 Transmission, 4-Speed Aluminum Sebring Type Racing, SK4516 QK Ford B/W Ea 381.35 266.95
C2AZ 7039 C Transmission-Housing For Tail Shaft BWT-10-B7 Strong Competition Warner Gear Ea 36.63 35.64