It'd be an interesting build, I'll tell you that. Since the Capt cards are supposed to be vintage, they would be made of old types of print paper. They should also be recreated, such like the image above, with a yellowing to show aging. Older newsprint (which is what I think older comic books are made out of) deteriorate and turn yellow, maybe the cards are supposed to be old newsprint? Just splurging some of my random knowledge on you, but don't take my words too seriously because I'm am by no means a "pro" at this stuff
Some members here have taken stabs at these. I heard that one or two have gotten Requests from EFx to stop.
I am sure that these cards were not printed on newsprint paper or any paper for that matter. Cardstock is what is used. I have some old Baseball cards from the 1920's and they are on cardstock. Coulson's Captain America cards were most likely printed sometime in the 1950's or 60's.
I have also heard that a few people that were making these have been asked to can it by Efx. I'm almost sure that the graphics on one project were more or less completed, but were never released for this reason.