I used inertial reel shoulder/lap belts in my 320. They were just under $100 each. I haven't crash tested them, so I don't know how they measure up. I expect they compare to four point belts and do worse than five point. The inertial reel is fastened to the outboard wal,l aft and low, behind the seat. The belt threads from the reel up to a pulley, behind your outboard shoulder, then to a lap-belt snap and then to a hard point beside your outboard hip. The receiving snap is at the center console. They work perfect (again, they haven't been crash tested). Everything is out of the way. No baggage space is used.

Bill Kennedy
N42BK 255 hours