3 point seat belts. 75 blazer with top off.

[eighteenninetytwo]

Where do I attach them? I thought the two floor points and the front roll cage. on another forum someone said I shouldn't do that (belts should be attached to the same thing ie the frame) but thinking about it. If we are in a sitch where the roll cage is shearing away and ridding me of my third fastening point I think I am pretty much D.E.A.D anyway. This is a mall crawler / classic car - not going anywhere off road beyond a beach or dirt road. any thoughts? How have other people attached 3 point belts with a top off using the original seats?