M122 = 2.0 L blower displacement...( 61 ci per L). The 07-09 shelby GT-500's all used a twin 60mm TB (FRPP sold a twin 65mm tb that drops right in).The Eaton M122 1.9 S/C was also fitted as original equipment to supercharged 2007-09 Shelby GT500 5.4v models which also retain the OEM TB and are also fully compatible with any aftermarket CAI designed to fit an Eaton Roots style or Whipple twin screw S/C. The point is, both the Eaton and Whipple designs are also positive displacement S/C's which are in fact, also very compatible with any aftermarket CAI as well. At any rate, also to my knowledge, the Saleen series VI S/C as you also brought up, is indeed the only PD design that does in fact retain the OEM TB for the 4.6L 3V models.
The 05-10 GT cars with the 4.6L eng all got the twin 55mm tb. ( FRPP sold a twin 62mm TB). 05-10 GT cars with roush M90 / TVS-2300 PD blowers all used the oem twin 55mm TB. I replaced my twin 55mm with the twin 62mm...drops right in.