I took the lap belts out of the EC a while back and notice that the thread pitch on the eyebolt didn't match the factory seatbelt hole. I think the bolt was fine thread and the hole coarse thread.

Do they make different pitch eyebolts?

How do you mount the shoulder harness in an El Camino w/o a role bar?

When is the antisubmarine belt required? Sub 12.0's?

How do you mount the shoulder harness in a coupe?
My Camaro will make it to the strip long before the EC.

5 point harness 12.0 and quicker,and yes you need the crotch strap too...I am still using the factory 3 point seatbelt,with no complaints from the tracks yet, neither track that I run at are sanctioned,but they seem to use rules from NHRA and IHRA. You have to anchor the shoulder straps to the floor with no rollbar,I think they make them extra long for that purpose. One track uses 11.79 as the break point for a rollbar and the other uses mid 9's in the 1000ft. The 11.79 track told me to slow it down are get a rollbar in it,thats when I went to the 3" pipes and mufflers. I used to race with open headers,but have since run a best of 11.85 thru the exhaust on drag radials.