Alfredo, Marichal would be a good choice. Bob, those were some tremendous pitchers! I am probably starting with early Spahn, Feller, and some 1950s Koufax and some of their contemporaries and then work back in time a bit. Ralph Branca and Dizzy Dean have some cards I stumbled across that will be included sooner or later as well.
Just looking through my Standard Catalog and hunting on ebay, I have located quite a few interesting regular and regional/team issues of Spahn and Feller in particular. As I have said previously, these guys are reasonably affordable when considering their level of accomplishment. This is going to be fun!