A safer alternative to just lap belts is available from Wesco. Wesco offers two 4 point seat belts (3 mounting points with a Y strap).
Installation instructions (available on product web page) show this require a floor anchor be added for each harness. This means drilling through the floor board.
Two styles of latch are available to choose from (flip up chrome, or push button) and 30 colors of seat belt webbing.
https://www.wescoperformance.com/4-p...ckle-help.html