But yet you're looking for a harness that involves either a lone bar welded between the B-pillars. (or that's brought vertical down behind the fron't seats so it doesn't interfer with the rear seats, which is a terrible idea if you haven't learned that yet).
You could mount the shoulder straps to a rear selt belt mounting point and the waist straps to the factory 3-point mounting locations. You'd only lose use of the driver's side rear seat.
What's your reason for feeling the factory belts are inadequate? Is this for safety, staying-in-place on track days/autox, or appearance? If it's the first, get it done right. If it's the second, then you could simply remove them when not in such an event. If it's the third, then...well...good luck.
You're trying to retain the side impact airbags yet are willing to throw away the fronts (which rely on the factory seat belt tensioners to function properly). You see the obsurdity in having a full cage in a street car yet not the obsurdity of a racing harness. I'm not trying to be a dick, your logic just doesn't seem to make too much sense.
::shrug:: Your life. Insurance is going to deny your medical claim either way with modified safety equipment.
