First off, absolutely agreed with the original list. Killer, Carew, Kirby, Joe—I can't really think of any way to move any of them off it. That said, if we included the Senators... well, Walter Johnson would have to be on it at the very least. My early baseball history is hazy, but Goose is a familiar name.
Then we have a difficult task though. Mauer has the least postseason success, but he's a Twins lifer, should be a surefire HoFer, and a Minnesota boy through and through. Kirby has the least WAR, but he was an excellent player and led us to a championship. Carew has the most WAR of any Twin as a Twin—Walter was a Senator—and was a damn good Twin (fun fact: Calvin Griffith's awfulness and trading away Carew led to my dad taking a hiatus from being a Twins fan). And Harmon... well, he hit 573 home runs (granted, 14 of them were for Kansas City).