Are you completely confident that mounting to the stock hollow cross brace is going to hold you in your seat safely? The seat belt mounting holes are meant to restrain you but that rear cross brace was engineered to match its name.
At most I trust the MA Motorsports harness bar for a street application since they actually mount frame/body bolt. I don't like to risk safety.
https://grassrootsmotorsports.com/fo...r/26305/page1/
Good luck!