The   PRC-77  can be modified for noise squelch, I offer several alternatives including purchasing a module, using the MICOR squelch IC to build a board and actually modifying  the squelch modules (either version)  them selves (requires soldering skills    )-  When a "new" radio arrived you had to use 100 MPH tape  to keep the switch in the ON position. Tone squelch was a stupid, expensive, often dangerous  over engineered  program.
Z

http://k4che.com/PRC77-Squelch/PRC77-Squelch.htm