For my 2cents, seatbelts are cheap (starting at 17$ at O'Reillys), I wear them all the time.
I have hit the windshield many times in the Attex's and Max until I put them in.
My throttle stuck in Busco last year as I was going up that first man made hill, I was airborne on the down side, bent an axle when I hit ground, but stayed in the seat.
Bolt them to the frame somewhere, retractable's are nice to keep the belts out of the chains.
Superior Safe-T-Products™ 46-3250B - Seat Belt | O'Reilly Auto Parts