ViperGTS, good to hear it is imminent..
I would leave the standard seat belts where they are. Hook the harness up to the cage or harness bar point.
Are you only running a 4 point?
The only thing on a 5 or 6 is the crutch strap, the lower seat cushion looks to be in one without an access slot, is the floor strong enough?
If you wont drill the PU for numberplates (understandable) will you drill the floor for a harness bracket?!