Lancer033

My current harness is due up for replacement (Crow 6-point clip-in) Since I've left it in the car full time since last summer, I might as well do a permenant bolt in harness (I'm assuming that would be safer). I'm looking at a Sparco 6-point belt with pull-down lap belts. I know the anti-sub belts are bolted to the metal bar in the floor where the rear of the seat is bolted to, but where do you bolt the lap belts too? Can you bolt the lap belts in and keep the OEM 3-point belt too, or does that have to go?

If it matters, I have a Sparco Evo seat on Speedware mounts, and a B-K Harness bar