I recently completed restoration of an R-390/URR receiver that I have had sitting in the garage for the last 10 years. The entire process took about 4 months of spare time. The unit was completely disassembled, cleaned, reassembled, detailed, and aligned. It is probably the best performing receiver that I have had the pleasure to operate. Take a look at the innards from the top. The tuning mechanism is one of the most elaborate mechanical creations I have ever seen (let alone worked-on!)

Here is the unit with the modules removed

These receivers have been used by the Military, the CIA, and the NSA since 1951 and were also used during the Apollo space program. I recently heard that there were a couple still in use at a Military post in Iraq.

The picture below is supposedly of a unit that was used during the Apollo space program

Here are the applicable manuals for this unit:

TM_11-5820-357-10

TM_11-5820-357-20

TM_11-5820-357-35