I am afraid that the brackets will not hold up in a wreck.

I agree, I have the same concern. If I go that route, I'll either mount the retractor's tab directly with the existing bolt, or fab a small bracket with a very minor bend (~15 degrees)in it so that the retractor will clear the curved roof section near there. That way if there is a big "pull" on the retractor, I won't have to worry about the bracket twisting and bending.

Thomas, I am really pleased that you seem to have elected to go the competition harness route as no standard belt will compare to the firmness and resultant safety of a four point harness in autocross.

I would even prefer to use them on a normal road car as I am quite a large guy and find that conventional retractable seat belts do not retain the initial firm feel that we would want at the point of any impact - our Zeds do not have pre tensioners like some modern cars. Videos of crash test dummies in vehicle incidents show that they move around more than enough with the belts taking up tension on the body so we hardly need to start with a restraint system that is not firm.

I am not recommending that we should all move away from retractable systems as my thoughts come from the perspective of a person with a body shape that it is not compatible with the initial fitting of a seat belt retaining its firmness, and is aimed at the original question from Thomas who is thinking of using his vehicle for autocross.

I do not think we have anything less than lap / sash (shoulder) belts in Australian Zeds and I think that all came out with retractable belts. It is interesting to hear the comments on options available to the North American owners.