What do you mean by "real" Vietnam style?
The first and second style would have some real value, especially if you shipped them south. You might get a couple of hundred bucks for the handguards alone, if they are a nice, matched pair. The third style would be worth much less, maybe $40? And the fourth style, which is what the vast majority are, are $15-20 for the handguards, maybe $25 for the stock. I bought a third style pistol grip at Milarm last summer for $5, they had at least two. I also have a second type pistol grip that was sent to me when I ordered a $3 "m16A1" pistol grip online.