Looks like someone did a stain themselves if I had to guess. I have a pair of decorator Cornwalls that the previous owner stained. Similar wood grain so I'd go with Birch
birch veneer with a badly done job of oil walnut stain wiped on with no sealer coat which accounts for the uneven absorption and color. Back in the day the go to finish was either a varnish or a poly urethane (pretty much the same thing. Hard to say but at this point you can coat them with what ever you want. Too bad by now the birch would have taken on a spectacularly rich patina had they been clear coated. Time to go to a wood worker and have them re veneered anything you want you can make them look better than new.
you do realize these just shy of 40 years old? So your caps are well past due for replacement. Stick with oil/film motor run caps so the sound will stay the same then you will be good for another 40 years. Bob Crites can sell to a new set of very much superior tweeters for these that would be a plan as would a fresh set of rubber gaskets for your mid driver (Bob has them also). Enjoy. moray james.
I also say it was raw birch, that was stained in darker color later.
I actually like it, and, depend on the smoothness of the finish, I will either do my silky-smooth finish, or leave them as is.