From what I remember, backed up by looking at Mustang vacuum schematics online: 1968 - 200, 289, 302 had Thermactor with MT, IMCO with AT. 390 and 428 had Thermactor regardless of transmission. 1969 - Thermactor remained on the 428, everything else was IMCO no matter which transmission. 1970 - 428 finally loses the Thermactor and gains the IMCO system, which explains your Cougar. I owned a 68 302 4V 4 speed from 1977 to 2001 and it had a Thermactor. Interesting noises when backing off of the throttle when cold.