MacArthur/Halleck (R): 297 EV
Truman/Barkley (D): 196 EV
Thurmond/Wright (Dixiecrat): 38 EV
MacArthur runs a far more aggresive campaign than Dewey did in real life. He attacks Truman relentlessly on the issue of Soviet expansion and Truman responds belligerently. This serves to alienate some more liberal Democrats and thus Wallace would have done a little bit better than he did in real life. Wallace may break 2 million votes, thus finishing ahead of Thurmond in terms of popular votes but still fail to break into the electoral college. Wallace's percentage in New York would increase from a considerable 8% to 10-15% of the total vote of the state. This is what tips New York to MacArthur and with it the election.
A President MacArthur from 1949-1953 creates a great deal of alternative paths to follow. Truman, in our timeline, intervened in the Korean War and did not rule out nuclear strikes. This was primarily for effect. However, President MacArthur may not have simply thought about usage of tactical nuclear weapons in Korea or to save Nationalist China. This creates a Cold War scenario which could become quite hot and quite soon.