An interesting vintage ATM Maksutov came into my possession recently. It was built sometime in the 1960's. The make is still unknown to me, but I am chasing leads the best I can.
The front meniscus measures right at 4" of clear aperture. I am not sure if that indicates that the primary would be the same diameter. I have not opened it up to look at the mirror and don't have any plans to at this time.