You might want to check, but I don't think all RT 328's are 720 channel radios.  I think just the RT-328 D/T were.  Cessna had the later RT 385 that were digital and 720 channel.  You are now required by regulation to have a 720 channel radio if you use it to transmitt.  You might want to check on that.  However, if they are and they are working, then I don't think you would have to replace them.  However, I would not bother putting any money into them on a repair when you have something go wrong.  As you probably know, digital flip flops will reduce your work load.  Good luck.

I bought a plane with the original cessna radio's, one was a 720 channel and one a 360 channel and the ADF.  I knew I had to replace the 360 channel, I fly instruments and one radio, especially old ones won't cut it.  So I bought a new slide in replacement (MX-300) for ~$1400.  Since then I had to replace the indicator on the ADF, and it works OK, but the ADF is a little weak on the 200 range frequencies.  Nevertheless, it makes for listening to AM radio stations when the controllers are boring me with planes at my 12 o'clock (I'm kidding!)

The other thing to consider is the age of the wiring and trays.  You may be faced with replacing all your wiring to get rid of the bad grounds, interference, etc or you may be lucky and it will work fine.  The GS/LOC and VORs are fine on my plane.  I have intermittent reception problems immediately after takeoff.  Give it a few minutes and no other problems.  I think it  is weak connections on the radio's at the pins, that get disturb upon takeoff, but settle back later.  It is not reproduceable on the ground so asking a radio tech to look at it would be costly and probably not work.  I would get the standard answer, it's time to rewire your electrical system.  What do you want for a 30 year old plane!

Hello,  I read in a back issue of CPA about a radio shop that repairs/tests Cessna radios for a flat fee of $75 each. Does anybody recall the name of this company?  Thanks,  Jeff     jeffstanford%tds.net

Sometimes common knowledge is incorrect. Radio Ranch still works on many older
FCC and FAA legal radios. Evaluation is usually less than $50.
This is not an advertisement. Just clearing up misconceptions.

Found this site. radioranchinc.com

Does the RT328 and the RT385 use the same tray?