My LDS is renovating to a smaller space. He has several vintage tanks that have come in over the years. Several are 1/2" NPT valves.
There is a real nice Sportsways with the decal in good condition and a nice Voit 1967 Swimmaster with an decal in excellent condition. Most have the epoxy coating inside. The tanks I have looked in seem ok but its tough to see pitting with the brown epoxy coating.
I have put up some pictures and videos of them. Reasonable offer + shipping. If you are interested in one with the valve on I will pop it off a nd get a light down it. They are of course as is condition.
My shops policy is the coating has to be removed before he will inspect and hydro a tank, he doesn't have a tumbler and it becomes cost prohibitive to do.
If you have an interest in one let me know. via the forum.