When you get closer, give me a shout and I'll point you to info you'll need to properly design mounts and rollbar harness mount, as well as suggestions on harness/belt designs. If you intend to do any sanctioned racing the FIRST thing to do is get a current rulebook, and read the requirements VERY carefully. I don't know how many times I've seen people build somrthing only to find out it doesn't meet the rules.

 

A long time ago I saw a study by DOT or similar, that concluded it was worse to have a weak 3-point belt system than a good lap belt. (Scenario was a shoulder belt that held you initially, but failed mid-way thru the crash event). This was specifically about retrofit 3-point belts. Looking at the structure of my '52, I don't see how it could credibly be modified to restrain the huge forces that a high speed crash (40 mph + ) could impose, there is just no structure that is tied to anything really solid. I've seen the home-made brackets and the similar kits, but I don't think they could possibly meet the same specs as a modern car's 3-points. I don't doubt they are adequate in a 25 mph crash. A roll cage would provide the structure but I'm just not going that way.

Has anyone got any real-world experience with the retrofit 3-point's performance in a crash? (I kind of hope not!)

For any belts, a good trick is to go to the boneyard and cut out some of the square, rolled-edge reinforcing plates they use on seat belt anchorages underneath the car. The rolled edges prevent the plate pulling thru the floorpan.

 

Racing product suppliers carry a good selection of mounting hardware that meet safety and racing rules and is inexpensive. Backing plates should be used on both sides of the floor and be at least 4" square, 1/8" thick. Mounting bolts should be no less than 7/16" grade 8 with grade 8 nuts and washers.