The main difference is how the display unit commands the pulse width and timing on the radome. The R40XX uses a 3-state anaolg voltage, while the R10X uses a logical hi/lo two-state scheme. It works out that the R10X radome responds to the two higher states from the R40XX as one, and gives the longer pulse width as soon as the range setting makes it necesary.
I am looking for a 4KW R40XX radome to extend the range from 16 miles radius to 32. I'll also take another 1.5KW R10X for spare.. It will also do to modify the R10X radome antenna elevation +12.5 degrees so that a better scan of the sky is accomplished and the beam is not reflecting from the ground causing clutter. These Raytheon units were made by Furuno. I maintain them myself. I have counted cows in a farmer's field with this, pictures later. BTW it requires an FCC license to use this kind of gear.