Ford Repair: e 150 rear seat mount, rear bench, conversion van

Question
i have pulled the rear bench out of my 99 e 150. there are 4 floating studs (they move) in the floor. i want to remove these. the backing plates are hefty and show no sign of looseness. before i get brutal; do you know how these come out?
it is a conversion van but i hope they used oem mounting.

Answer
Hello and thanks for the question...I'll try to help.
Sorry, that is more of a body person question......I'm a mechanic. IF you are not going to EVER put a seat back in....why not use a cut off tool and remove them completely?
Hope this helps,
Erik