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I've got a DJ four point and have made several mods as I had the same problem. First off, it didn't fit around my stomach too well, plus it didn't allow me to remove my rear panel behind my seat when I wanted to.
So I installed an eye bolt (from DJ) on the outside body latch point to be able to attach a quick release latch I installed on the harness in place of the stock end on the harness. While doing the switch of the new latch, I used some of the old seatbelt as extra strap to lengthen the harness half on the lower outside about 8".
Then I cut the stock end off the inside half of the harness and had a shoe repair shop sew the quick release end of the stock seatbelt on to the harness using another piece of old harness. Since the two cables stick up from floor about 8", I ended up with that side being about 6-8" longer which gave me enough to have some slack around my stomach. This also allows me the ability to unlatch my harness from its base on the inside (which is now the stock quick release latch) and flip it back so I can remove the back panel completly if I want.
It's important to note that seatbelts are all right handed, so be sure you sew the new harness ends on the correct sides of each harness--they will be just the opposite on one side. Otherwise, you will have to strip out the threads and have the shoe repairman do one set over. (Don't ask me how I know this!)
GJRonK