Oh gosh, you can't be serious your friend said that! Don't confuse people by saying "you can attach it anywere (anywhere) you want". Your statements are misleading (at least in English). Did you misunderstand him or something? Sure it's ok for the lap belt bolts to go to the floor, but not the shoulder harnesses to go directly. That's a NO-NO! The downward force would crush your spine. You can mount the shoulder harnesses to where the rear seats used to be or even better is to mount it at a 90 degree angle to a roll bar (or part of a roll cage). Just attach the shoulder harnesses right to the bar. You don't have to go over the bar and then to floor! That's more of a chance for the harness to get cut in a serious side impact on the street.
Be careful what info you pass on, even if it is hearsay. You don't want to kill or paralyze other people on here.