I'm putting in 4-way harnesses to go with some Mazda 3 bucket seats. I have brackets made to mount the belts, but the frame gets in the way of bolting them down. There's a threaded hole on the passenger side, but not the driver's side. Can't find a bolt with the right thread size anyway.

Would welding by strong enough to hold the brackets? Or is there any other tricks to mount them?

(the floor boards are brand new, from NPD)

Anyone?