I've seen roller kits on Ebay for older Mopars on occassion, not sure about the '60/'70s stuff.
Just found a rollerbearing conversion kit on some Australian site, but at $130 I'm sure some thinkering in the garage could come up with a cheaper alternative.
I've converted the idler arm bushing on my '57 Chrysler to 2 nylon halves some years back;