Only have experience with 1966 Rancheros. The '66 Ranchero is based on Falcon, so I used parts off a Falcon. Find out what your '79 is based on and go from there. I think it's based on Fairmont, which shares the Fox chassis with the Mustang if I'm not mistaken.
Whoa, whoa, Not big fords either. 72-79 Rancheros are based on the Torino/Montego platform that started using a full frame in 72. So, standard clutch linkage from 72-79 Torino, Montego, Grand Torino, Ranchero & LTD II would work. I dont remember the last year for the 4 speed option in these though, I dont remember seeing any after about 74 or so. I have seen some on ebay, they go for about $200.00. Good Luck