Is it possible to mass associate the existing cad & WTPart with different version history

You may use Compare Part Structure Action, you will get Build Association between CAD and WT Part.

Go to Information icon of CAD Generic Part or Assembly --> Click on Action --> Click on Compare Part Structure --> In Compare Part Structure Tab you will get Build Association Icon.

If they are in your workspace you can select all 48 objects and associate them to the wtparts by using the auto associate or associate command.  As long as your numbers between the CAD and wtpart are the same it will find them and create the associations.  Similarly you can do this as well when checking into commonspace by clicking on the auto associate option when you check-in. 

The versions between CAD and wtpart doesn't matter, it will associate to the latest.