In the bottom left of the image you have what appears to be the "blackout driving lamp" that you might have found on the Willys MB, or "Jeep". However the bonnet of the vehicle doesn't look right for the MB. Stepping through the successors to the MB, you come to the M151, which has the same front-to-back ridges found in the photo and an overall shape that bears a strong resemblance. According to the wiki article, these first entered production in 1959 and first saw service in 1960.
Three major variants of this vehicle were produced, the M151, M151A1 and M151A2, with the only differences that might have been visible in this photo being the indicator lights. It is hard to be certain, but I believe that from this high angle, with so much of the blackout driving light visible, even the smaller indicators of the M151A1 should be visible. The A1 was introduced in 1964.
I would suggest that this puts the photo somewhere between 1960 and 1964 plus however long it took for the newer models to filter through. Exactly how long that might take is just guesswork. Although this window places the photo during the Vietnam War, American involvement was not yet at its peak in 1964 (16,000 troops vs. the peak of half a million in 1969), and was at the beginning of a substantial "ramping up". The US presence in Korea in 1964 was substantially higher, but fell over the same period. With evenly distributed upgrades, the number of M151A1s in Korea might have exceeded the number of M151s by about 1965. However, if priority for new equipment was given to forces operating in Vietnam, then the A1 might not have arrived in Korea until several years later.
Probably early-to-mid sixties, possibly later, but unlikely to be earlier than 1960.