No worries and that is a sweet rad set up!
Those MM look just like the AA ones. Perhaps use and how the truck is driven has to do with how fast these wear out. The ones in my 80 are probably 10-12yrs old, conversion done in 2002 and I suspect they are original. But they are wasted now.
IMHO, best MM you can do is a custom one made from a vulcanized leaf spring bushing. Super strong, cheap and you can always find a new bushing anywhere if you need one. Plus if it blows the rubber it can only move 1/4" of so. Thing is though not a lot of dampening in this style.
Like I said, I stood next to my 80-chassis last night after posting and realized I was wrong. Just more used to the older trucks with the thinner inner rail. The 80 frame is way beefy and very well built. One of the major reasons I am using it in a build.
Cheers