I have a 70 Blazer that originally came with utility buckets and no rear seat. I too also have no bolt holes to mount to, so I guess I'll just have to drill some holes so I can mount the seat I bought in.
I had bought a few of these packages awhile back to use underneath the bed as a simple way to drill a hole and mount the bolt into the threaded anchor bracket from underneath. They are made as a reinforcement for seatbelts, but I figured it should work for this as well.
http://www.thehoffmangroup.com/autol...so?itemid=sbhp