Here is the top 10 in all games
From 1939-51, here are the AVG-OBP-SLG for both DiMaggio and Williams in neutral parks (with Fenway and Yankee Stadium taken out)
Yes, Williams beats DiMaggio in SLG. But it is fairly close, much closer than their career numbers. So under pretty much the same circumstances, DiMaggio slugged close to what Williams slugged. The big edge is OBP for Williams.
Now only looking at neutral parks leaves alot of PAs out of the analysis. But DiMaggio's stats put him almost on the level of the guy many say was the greatest hitter ever.
Data from Baseball Reference and the Baseball Reference Play Index.