'and will last pretty much forever'
I doubt that. If you notice, the tang of the mount that fits in the frame bracket hole is where the things fail. There needs to be more side thickness or depth on that hole. The body of the mount thickness is adequate for the bouncing loads but there are side oscillations which the original mount don't adequately handle. Some years back, the mfgrs did a better job with the mounts.
I have the cab off of a 93 and was looking at the problem. There are larger mounts made by Lord which are common on engines in industrial applications. It is my intention to modify the bracket on the frame and use those. I don't have a number or any other recommendation at the moment but I plan to get something done on that next week. If I can firm something up I will post what I find.
Incidentally, I found a crack in the frame on the passenger side at the lower rear edge of the front suspension crossmember. You would never see it from a casual observation. In fact, I have had the cab off a couple of weeks and the engine out. I only just noticed it. This was a Texas regular cab flatbed truck that I bought for parts. Can't say at all as to the way the truck was treated. It only has about 180k miles. I plan to look real good at my others when they are on the rack.
James