Mounting brackets for bucket seats are different from bench and bucket seats. I used an original set of 4 rear brackets which were used as a pattern. I had a local company manufacture them for me. I have some extra sets that I'm selling. They are in very close to the originals. The brackets on LH side of the picture are used for the passenger side, and the other is for the divers side seat. 

These should fit the following:

1969, 1970, 1971 and 1972 Chevy Pickups.

1969, 1970, 1971 and 1972 GMC Pickups.

1969, 1970, 1971 and 1972 Chevy Blazer.

1969, 1970, 1971 and 1972 GMC Jimmy.

1969, 1970, 1971 and 1972 Suburban.