i have used a muffler clamp welded to the side of 1/8 flate plate then drilled and tap the plate for 8 32 screws and bolted thru the fire wall and used some flat heads thru the floor or weld . the other way i don it was find a tube 4inch long that the O.D column will silde thru and weld a plate to that so that can be bolted or welded to the floor and fire wall then i just use a self tapping bolt to keep down any thing moving