I have only done the bench --> buckets in an 84 cutlass but I think if you loose the bench you will need the 4 inner bucket seat mounts, two on either side of the trans hump as the bench doesn't use them.
I used wood blocks and HUGE washers on the underside of the floor pan
I think the hardest part about switching to bucket seats is actually FINDING bucket seats
I tossed the split bench in my 85 cutlass for buckets, but I could only find Camaro buckets (redone already with the GN theme ironically). They're about 1 inch narrower, but I was already welding in floor patches so welding up new seat mounts wasn't a big deal.