If you go to a harness go 5 point. 4 points without the submarine strap are a waste IMO. I was in a multiple times barrell roll a couple weeks ago and driver was not wearing his submarine strap (he was a large guy and it was uncomfortable for him). Even with our helmets and safety gear on he separated his shoulder and was concussed from moving around and hitting the cage. I was wearing all 5 straps and other than being sore I was fine.
And if you do go to a harness, you have to put a cross bar in behind the seats (which can be a hassle if your backseat is used often). From a safety perspective that is the only way to do it right. I believe there is a Billavista article on Pirate about it and also there might be something on Mastercraft website about it.
Thank you Dave Cole, Dynomax, Falken and all the Spec Class sponsors!!