For Sale: Cooltech LLC harness clip set (both seats). These are used but they look brand new. These will allow you to mount a sub belt without drilling through your floor. $120 shipped.
http://www.cooltechllc.com/ford-boss-302-parts-accessories/71--harness-clip-set-single-seat.html
http://www.cooltechllc.com/ford-boss-302-parts-accessories/71--harness-clip-set-single-seat.html