Jon: I am the previous owner of your D304 Cobb. It resided happily in my set for the past eight or nine years. I had a second one, an "Authentic" that presents as pristine, so decided to let Al have a go with the SGC20. Don't remember what I paid for it but I think it did pretty well. You did just fine; I don't think D304 Cobbies will ever diminish in desirability or value. Good luck with the rest of your set. Some beautiful cards to be had. Tenney was the big toughie for me and Young wasn't easy either.
My set:
http://imageevent.com/kawika_o_ka_pa...4brunnersbread