There are a lot of little details on Corvair installations that are best shared in a picture and a few sentences. Below is a distributor clamp, installed as we prefer, on a 3,000cc corvair that we built.
Above, the proper orientation of the three parts of the distributor hold down.
Every now and then I inspect a Corvair engine assembly where the builder has the incorrect clamp, or has it improperly installed. First the nut; the stud thread is 3/8″-24. In its stock form, the nut is a regular fine thread nut. In the car it is unlikely to back off because the little wire clamp effectively spring loads it. In the plane we are not going to count on this. The best nut for the job is an MS21042-6, something you can get from any aircraft catalog. A regular all metal lock nut will often have it locking feature above the top of the stud. The MS nut is low profile and the fact it takes a 7/16″ wrench makes it easier to tighten. (This is the same nut we use on the hybrid studs to hold down the prop hub.)
Under it is the stock GM square washer. It has two little ears that face down to keep the wire from spreading when you tighten the nut. A regular washer will not work here.
Under it is the GM wire style clamp. These are far better than any other type of distributor clamp. When you put the pressure on them the two ends of the clamp make very firm contact with the distributor housing, and then the wire deflects as a little spring. I have never seen one of these move once it is tightened down. The reason why the two parts look shiny is that we have the ones on engines we build nickel-plated for corrosion resistance. A quick shot of spray paint will have the same effect on engines assembled in home shops.