The lug nuts are not replicas. To be perfectly honest, I don't really know what the originals looked like. I do know that they were probably capped like Jim Lore has stated. GM did a lot of the lug nuts in this manner. The Rivs and Wildcat used 1/2 x 20 and I do have a stainless steel version available.
Jim, I always thought that they were chrome plated steel and the "cap" nut came later (at least after '68 o No. I have no facts to base this on though, I just thought that the lug nuts on my GS were original and they are chrome plated steel acorn style.
Mike I have no idea about a changeover date. I am speaking of experience from the 70 model year. I am pretty sure the originals were never stainless but they are a great substitute.