I have a cg lock, Just like the idea of a 4 point as i am giving my car the rs look as well as using it for the track days. so would like to try and fit one if possible. If you guys over there use 5 points how do you fit them i take it it must be similier, Thanks for info though any more thoughts, Cheers Tim.
Any harness with dual shoulder belts needs a seat with slots cut. Some shops can do this for you. I you want a safe setup the seats must be replaced with ones that are designed for dual shoulder belts either Porsche or aftermarket
There are 2 problems with your proposed set-up: first, without slots for the shoulder harnesses, the shoulder belts can be dislodged, or slip off your shoulders in a crash. Second, without a sub-belt, you can't effectively tighten the shoulder belts anyway, without causing the lap belt to ride up above your pelvis (which is not good).
I agree with those above that either a CG Lock with the stock belts and seats, or some seats with the appropriate slots for 5/6-point harnesses would be safer. You might want to check with member Tess Tickle at Motordrive.com to see what he has to offer in the way of aftermarket seats.