OK, about the rules, just don`t understand that.
I did 2' square tubing inside the rear frame as shown in a post above, fit in it perfect w/ a little messaging. The front I used plate as normal, bolted up to the trans. crossmember , while getting the rest done, then welded that too. They are cut in to the floor full length, and welded there too.
Very stiff, and look like they belong. I did use 3/4" foil faced foam board to build the floor level even w/ the top of the bars in the interior, before covering w/ new carpet. You cant tell they are there. My home made driveshaft loop is welded to the new frame rails. The roll bar plates/mounts are welded to the frame rails and the floor also. The rear seat bolts go thru the driveshaft loop , pretty strong set up that doesn`t weigh any more than the normal ways of doing it. The raised block 505" fastback only weighs 3273 w/ 1/2 tank of 91 lawnmower gas , w/o me in it.