There were 1903a4's used in Vietnam but I never heard of one as with the plastic or fiberglass stocks. None of the reference manuals I have seen ever mentioned one.
If one does exist, it is something some individual put together but nothing official.
I think the drill teams 03's had fiberglass stocks...guys that did the rifle spinning. As to "sniper" rifles, all that I'm aware of were walnut stocked
I know of two that were in the possession of MACV/SOG Kontum in '67/'68. I watched two old E8's bring one up on a water tower and have a go at a small mortar. They couldn't hit within 50M at 400 yards we watched the shot falls with 7X50's. I'll give them an A for climbing up there with us and trying. From what I know now and not then I doubt they were zeroed in anyway.