Yep... there are a host of M16-equipped ranges out there, although very few ARVN. The early VC were almost entirely kitted out with US M1 Carbines, Garands and BARs, obtained via the ARVN and would double as RF/PF. Likewise US Advisers carried the same kit and M3 Grease Guns. US Army and Marines both used the M14 in the first year of the war (Marines later obviously), differing only in that the Marines wore flak jackets constantly.
That being said I would buy anything Vietnam-related by Mr Hicks... early period or otherwise, I'd just prefer to start gaming it from '62 onwards given the choice.