After some effort, I recovered my log-in info and am now back as "Douglas." Thanks to all for the kind words, helpful suggestions and inquiries. Here are my responses:
Material: Despite the hangtag from the manufacturer that reads "Lederware," the Hepco luggage is made from naugahyde/leatherette/vinyl. You'd think they would use MB Tex, but it's not. For what it's worth, it's strong material that is still pliable after 40+ years.
Selling 1 set vs 2 sets: I appreciate the suggestion. That would probably be the way to get the highest dollar figure, but I'm happy to let the auction run its course as it stands. Fitting the luggage is a modular task with different configurations for different models. For example, I'm guessing the early 230SL with vertical spare should be able to accommodate all 4 pieces in the trunk -- 2 stacks side by side and perpendicular to the tail panel with the large piece (option code 291) on the bottom and the medium case (option code 292) on top. There's also the rear parcel shelf for additional storage behind the seats, reminiscent of luggage storage inside the preceding model, the W198.
All in all, this is a pretty obscure option that is probably only of interest to people who like esoteric details and who get a weird sense of satisfaction reuniting old cars with old original options from back in the day.