The three B-17s were:
B-17G 44-83525 (N83525) from Tallmantz
B-17G 44-83684 (N3713G) from The Air Museum
B-17F 42-29782 (N17W) from Aircraft Specialties (air tankers)

The location filming was done at the airport at Santa Maria, California, in January 1968 and utilized both Tallmantz B-25 camera ships (N1203 and N1042B). They spent a day or two doing some air to air filming, and a day or do doing landing and takeoff shots, and also scenes with the actors around the airplanes.

Jim Farmer did a great little article about the filming entitled “Santa Maria Diary” that was published in the AAHS Journal back in the 1970s. If someone really wants to know which issue I can look in my files.

There are also details and photos in the book Final Cut, which also covers other post war films using the B-17.