No, the 68 Falcon uses the same upper and lower arms as a 69 Mustang. The 66 lowers are too short and the uppers have a different bolt spacing and I believe are slightly longer. I used the 69 Stang parts to rebuild the suspension on my 69 Falcon wagon two months ago, fit without a problem.
I doubt the rear leafs would work. The axle will fit, it's the same width as a 67 to 70 Mustang-59.25", but you'll have to run a larger backspace on the rear rims. I have a 67 Falcon rear I'm going into my 66 coupe next weekend so I can run late model Bullitt wheels without spacers (17x8" 5.72" backspace). The shocks are different also so they can't be used, at least according to the part numbers anyway .