I did dig into this a bit more the other day and learned that the "main RF can" is the cesium oscillator module. The history there was pretty interesting! The early ones I found were the Symmetricom Quantum SA.45s[1,2] which included a pretty entertaining thread here[3]. There were several levels of quality and function in the family of products which have been discontinued in favor of the MAC-SA55[4], and I wish I could find where I saw that recommendation... It's a rubidium, instead of cesium oscillator, not that I know enough about these things to concluded one should be better than the other but my impression was cesium was higher precision.