I have noticed some used the push on, and others(like mine) have a hole drilled in the rod. Wonder if it has to do with when it was built, or a frustrated PO? :: Mine was built Sept 64. The bronze bushing sounds like a good idea.
The little piece on the end is called an "axle nut". Hardware stores often carry them. I used two Palnuts ahead of the axle nut to make sure the rod never comes loose. A Palnut is a washer-like device with teeth on the inner edge. Pushing it over the torsion bar results in a locked on fastener. Axle nuts and Palnuts are hardware store items.
Why is it important to properly retain this spring/torsion bar? If it comes loose at the wrong time it can slap the car body and put a nasty scar in your paint job...I know...been there done that!
Now there is another variation. Those axle nuts sure as heck don't go anywhere when they are pushed on. I have already heard of a story of the bar coming loose and whacking the fresh paint... :: I won't mention names
Yeah, I almost became an alto singer when I started to take the torsion bar off. Then I realised that I didn't need to remove it to take the deck lid off. Lucky for me it only took 15 minutes of prying to get the thing back on.
The 66 assembly manual shows a push-on type fastener called a "spring nut" and lists it as # 380264-S2. It also states that "the torsion bar must be installed after the luggage compartment door" (their terms). There are other detailed instructions which I could send you in a PM if you want. In my case, I had the original push on nut, but I had previously removed it during the restoration. It's also likely that it had been removed several other times in the life of the car. Anyway, it pushed on OK and seemed to be holding. However, at a local cruise, there was this big BANG when I shut the trunk lid. It wouldn't open anymore either. At home, we were able to wiggle the trunk open enough to see what happened....the push nut had come off and the end of the torsion rod was wedged somewhere in the hinge mechanism, preventing the trunk from opening. Once things were recovered, I drilled the rod and installed a washer and cotter pin.