commandobolt replied to your photo “Two Australian soldiers at Dat Do compound, one wearing an AN/PRC-77…”
PRC-77 is the upgraded PRC-25 and came into service in 1968.
“The AN/PRC-77 set was an improved version of the PRC-25. Specifications and accessories for the two radios are nearly identical. The only important differences in design were internal; they are virtually impossible to tell apart externally.”
Additionally, the source identified it as such, and given that it was a communications unit, I think it’s likely to be identified correctly given they knew what equipment they had used at the time.