Sunil,
I put 2 swivel chairs in a 14' jon boat several years ago and it worked great. The only problem is if you try to attach the seat to the top only, the metal may not be strong enough. The best way we determined to do this was to buy some long threaded bolts and then put a piece of plywood slightly larger than the factory bench under the bench so that the threaded bolts go through the 4 holes in the base of the swivel chair, completely through the bench, and out through the piece of plywood on the underside of the factory bench near the bottom of the boat. In our case, we had to notch the underside of the bench just a bit to allow room to work. The result was an extremely strong mount that lasted as long as we kept the boat. We did not notice any "top heaviness" to this design and really enjoyed the comfort of these seats.
