Good buy Fran!
I purchased a "sister" set of the same wheels several years ago. My understanding is that Jongbloed made them in the early 90's. They used a center casting from a third party and Bill Jongbloed spun the rims for them. My set was also NOS that a guy had in his attic still in the original boxes.
They are the same size as yours. I sent the rears back to Bill to have 17" rims spun for them...left the fronts at 16".
I understand that Jongbloed has his own center casting now (magnesium). I think ERA purchased the molds for centers that you and I have.