I modified the rig for a vision-impaired ham- made at notch at channel 1 position so they could find their home channel and then move to the next 'channels' in the rig. Each 'channel' requires a transmit and receive crystal. I added a PL tone board to the rig and it had a keypad added to the back socket- which has several items available. Rig doesn't need much power as it is only 1W or 10watts, so I replaced the incandescent bulb with an LED bulb so you could run it off of a 12Volt battery for backup. Has a 'quick' channel button that takes you directly to the crystals installed in Channel 3. Other controls for hi/low power, usual rotary squelch and volume. Seems to do well as far as ignoring intermod compared to newer rigs. Paid $40 for it, with crystals, and it was worth that. Still in use by blind ham friend. Better than a menu-operated rig as I love switches and knobs to do the work. Only wrinkle is trying to find crystals for the rig. Old school that still works just fine. Don't like the downward firing speaker as you have to prop it up to hear, but does have a decent amp. Plug and play in 10 seconds, no manual required if you have the crystals.
I bought my TR-72 used in 1971 for $225. I've used it continuously since then as a simplex base station, mobile rig for US repeaters, and a portable back-packer in Europe. I’ve added (and later removed) both an outboard frequency synthesizer and an outboard audio-tone generator. The rig is currently modulated by a BYONICS tiny-tracker in mobile APRS service. The receiver (that still actually has a tunable LC circuit in the RF section) remains both sensitive and selective. The transmitter still puts out a flawless FM signal and in 42 years of hard use there has never been one component breakdown. What more can you ask?