I noticed with the addition of the Type 56 that the US and ARVN's M20 is absent. These two weapons are so similar that the inclusion of one without its counterpart seems a missed opportunity to produce more content with minimal additional cost. The M20 75mm Recoilless Rifle was the 'original' while the Type 56 is a Chinese copy built from captured examples from the Korean War. There is almost no practical difference and very little cosmetic difference between the two weapons, and most players would overlook a simple conversion. By removing the camo wrap and giving it a "coat of paint" reskin to Olive Drab, it would be virtually the same to the casual observer.
In the interest of meeting your quality standards, some small changes or improvements are, in my opinion, optional. The simple M85C sight for direct fire can be used rather than the more complex indirect fire sight the weapon also came with. This sight uses a standard US fixed reticle. It is worth noting it typically deployed on standard US machine gun tripods such as those already in game with your M1919 and M2 (although the book shows it mounted to the M1917A1 tripod 'trail legs front', that is, backwards), and it could fit a standard vehicle pintle and so it can also arm a jeep. The American shells were all of the standard artillery shape but included HE, HEAT and Smoke. This being WP Smoke, of course, for 'incendiary and limited anti-personnel effect' as the book states.
For additional reference, the 1948 field manual is available here. As AVRN troops received WW2 or Korean era equipment anything 'dated' from this book is likely still true for what they used. Even though this weapon was replaced in service by the BGM-71 for anti-tank duties, as in Korea it was a powerful direct or indirect fire weapon against positions and emplacement. It can even find use in Mike Force as an ACAV armed jeep or as a deployable static weapon, using the backpack and base system.