have you actually used a std seatbelt with a full bucket? not exactly the best combination tbh...
the seatbelt doesnt hug the body (unless your quite huge), the seatbelt just goes from one edge of the seat to the other so you not held in by the seatbelt around the waist...
and yep the buckle is mounted on the rail but using a bucket its not exactly easy to get too, its quite a way down the side unless you make up some sort of extender plate so it sits higher...