The drivers side inner seat mount or slider is shorter in height on 75 and 76 a bodies, due to the hump in the floor to clear the catialitic converter. That might be why the seller thought the mounts looked as though they had been modified. The mounts from earlier a bodies will bolt to these seats or you could fab up a spacer for the shorter mount. I have a 75 Duster that I put 73 buckets into and I found the 75-76 mount on ebay. My Duster was a /6 with one convertor, but the 360s may have been built with twin converters for dual exhaust, I'm not sure.