All the usual parts suppliers carry the rubber bushings  and do not appear to offer any alternate bushings such as the steel ones you have, and that includes CJ-2As, 3As, and military models. Not an exhaustive search, but enough to verify that those are pretty unusual. I pulled the rubber bushing out of mine this morning to begin rust removal and it was so dried out that it just crumbled. Maybe the steel is a good idea.

Rubber is cheaper than steel and probably does provide some vibration damping, not a bad thing for a heavy generator hanging off the side of your engine. On the other hand, if you live in a hot, dry climate you might want to replace a rubber part with a steel one if it was practical to do so. I'd guess those bushings were custom made, but as soon as I do that someone will identify them as WWII parts manufactured when rubber was scarce

During my restoration 6 years ago I ordered from one of the Jeep sources, a couple of the rubber bushings.  They were so poor that I ordered a couple more from another Jeep source.  They were just the same, very poor quality and very soft.  I ended up putting the old rubber bushings back in that I was planning to replace.  I don't know if they were original (most things on my old Jeep were original) or if someone had replaced them somewhere along the way.  They are rubbery but firm.  I like the way they support the generator much better than the new ones.