My Plainsman bulk CO2 shotgun has a walnut stock, like all Goodenow production (per Larry,) so, there is really little question that it's a Goodenow gun. I believe what Fogel told Larry that Plainsman (California) never produced the bulk fill option. That leaves it up to Goodenow to have produced them.
However, as of this point, nobody has ever found any original Goodenow literature of any sort to back up anything. There is one small magazine ad but that's the full extent of it, as far as I've ever seen. My experience has been that without original literature of the company it's very hard to produce a precise history. When interviewing people for my Crosman books, I heard all sorts of stories that didn't turn out to be exactly true.