Depends on how anal you want to be about dress and equipment. The TAG troops with M14 seem to be in tropical uniform and definitely with US Army style 1956 webbing equipment.
Marines, the principal user of CH-34s post 1963ish, were in OG-107 standard temperate fatigues, M-1952 flackjackets and M-1961, USMC specific, web equipment . You can see this in pictures from the initial landing at Da Nang through their first major operations like Op Starlite/Satellite. With the exception of the adoption of the tropical fatigues that's pretty much how they appear right through until late 1967 for the most part, although supply bottlenecks means that they increasingly use US bits or complete sets of US Army personal equipment by 1968.
I do wish someone would produce early war Marines, I really do, they would be suitable for other settings like the Dominican republic in 1965 or fictional encounters during the Cuban Missile Crisis.
Advisors can be wearing pretty much anything although early in the piece it's likely to be either OG-107 fatigues or with the more elite ARVN units some variation of the local troops uniform that they are serving with, so possibly Tiger stripes with the ARVN Marines, ARVN Airborne brushstoke, or commercial duck hunter camo fatigues. As their logistical supply came through the units they were advising it would be uncommon to see advisors toting M-14s, they weren't part of the supply chain and to be honest the M-14 never quite saw universal service with the US Army anyway, as production was slow and ulimately cancelled early. There was a minor scandal when the eyes of the world were on the US Army during the erection of the Berlin Wall (1961) and the resident battle group was seen to be still armed with WW2 era M-1 Garands.
Your more typical advisor weapon is going to be something in the ARVN inventory: M-1 carbine, Thompson, M-3 SMG etc. Batches of early model AR-15s were tested with the ARVN, so an M-16 armed figure is entirely possible.
Of course the usual caveats about the toys being mere avatars and individual choice on what to use.
As they say in the classics your toys, your choices.