The 66-early 70 Falcon's absolutely share the unibody with a 66-67 Fairlane. The 66-67 Falcon and Fairlane Rancheros are based on a variation of the 66-67 wagon unibody. If you look, a 66 Ranchero has a 66 Falcon front clip, and a 67 Ranchero has a 67 Fairlane front clip, but they are identical unibody structures.
An FE will bolt into a 66-early70 Falcon using 66-69-Fairlane/Torino hardware. All drivetrain parts interchange, and other than minor variations in the 66-67 style versus 68-early 70 style front suspension and steering which is common to all unibody Fords, those parts all interchange too. 66-71 station wagon and 66-71 Ranchero rear axles interchange, but the 70-71 rear axle is a touch wider. The steering column configuration changed in 68 to be a collapsible column for crash purposes.
My frankenwagon started life as a high optioned (V8, power disc brakes, power steering, air conditioning, power rear window) 69 Falcon Futura wagon, but now looks like a 67 Fairlane wagon after only swapping the front clip and changing the tail lights. It's been a few years since I did it, but I recall that the fenders bolted right on, and all I had to do to mount the Fairlane grill assembly was drill 4 holes in the embossed areas already stamped into the core support.
I say build it, there aren't enough of these bitchin old wagons left. If I hadn't saved mine, it probably would have been a parts car for a more common late 60's Ford.
Brett