@sourpuss123 Ah, what to do with a bone stock bit of historic kit…..
I went down same path w my family heirloom MX-110Z and MC240….
Disuse will lead to failure and so may use as you know. Real Marantz parts are considerably more rare than Mac bits, so finding bits to retain stock could be neigh impossible… so if you do modify w new rca, etc I advise keeping the old parts ! I did ultimately decide to have both of mine modified. The MX went back to Vestal to Audio Classics where retired Mac engineer Richard Modeferi went thru it, including a factory defect. While in the unit he incorporated his “ RIMO “ filter circuit in the tuner.
the 240 went on a similar path w a master Mac tech keeping it stock but fixing a few caps and importantly worn out input RCA, pots. I fell in with a Jim Mchane mac modification dude Mike Samra of Saginaw and he went thru the amp extensively w Russian PIO, Shuko, etc…. It is a fantastic sounding amp now….. The RM-9 slightly more accurate but the 240 is closer to my heart. i remember the day it came in the door in 1965 :-)
I think Mike or Mcshane would be good people to consult with in addition to Kevin.
Best to you on your journey