Several of us have installed a four point. I installed mine using the stock seat belt points for the lap belt and then used the long tang of the shoulder harness run under the head rest and then attached it to one of the rear seat belt clips by using a male end off of a junkyard seatbelt. It works really well, and I hate to say, but I did give it the crash test and came through unscathed (see contour rollover in auto-x topic).
Hope this helps,
Rick
