I know a lot of you recommend gettting 73-79 brakes to upgrade a 66 but what about using an 84 or 85 F150 Brake parts. My uncle has one just sitting there and wondering if the parts would work on my 66. Thanks.
No, unfortunately. Not even a close fit - although close only counts in hand grenades and nukes anyway!
Now the power booster and master cylinder MIGHT work. I know the rear brakes from an '80s Ford 9" can be swapped, if you use '72 axle shafts on the '66.
Check with AutoZone, Advnace or similar to see if the rotors and calipers are the same. If so, that might save some money. The bell crank for the booster might work too, but you will have to trial fit it to see if it can be made to fit. Seems as I recall when I checked this out, that it was a no-go also.