iam loving the way you are thinking the zu-23 along with the 14.5mm zpu-1, zpu-2 and zpu-4 would be great additions for nva ,viet cong etc and for any mideast types. Just not sure if they fit in with any of rubicons plans or ideas, and as a modeller would certainly grab a bunch.
On subject of aa guns a russian 37mm m1938 61 k was used from ww2 right up to present day and this does fit with the bofors types being developed