I am not sure how much the 60-64 Galaxie floor differs from the 70, but this info may be of some help. I installed buckets in my 62 Galaxie buy building a seat riser that bolts to the contours of the 62 floor and provides a flat mounting surface for the seats. My buckets came from a Subaru and the first thing I did was convert them to have the same bolt pattern as a Mustang sense I have a Mustang and wanted some interchangeability. The bolt pattern should be the same on the Cougar seats you have.
Converting Subaru seats to a Mustang bolt pattern
Once I had the track width I built a seat riser so that the seats would have a solid and level mounting point.

Here is the seat riser mounted on the floor. I used the two outside original bench mounts and then added two 3/8" mounts on the inside. The angle iron that the 3/8" bolts are attached to spans the floor and then a solid piece of 1/8" plat still goes on the underside of the car and serves as a large washer and floor reinforcemnt.

Here is a picture of one of the bucket seats installed

here we have it both buckets. They look right at home in the old Gal.