I find this interesting. It appears that John's mass balance weights fit significantly better than Pauls and that Pauls don't all fit the same. My guess is that the tooling is getting a bit long in the tooth - as they say.
I am attaching a photo of the 1992 version of the mass balance weight fit on my new Model IV and another of a weight I made after SKystar went bankrupt when there was some demand for some of the then unavailable parts.