Using a slash body on a stock rustler chassis won't work, the wheelbase is too short. You could get another set of rear arms and put them up front, that'll give you some extra wheelbase. When I had my rustler I was working on my own extended chassis to run a slash body, never finished the battery mount though.

The extension itself is 20 or 22ga sheetmetal, the rollcage is steel brakeline welded to it and attaches to the front shocktower for protection and less flex. Your front body mount can be flipped for more height, attach the slash rear mount and go. I did do some testing and actually like the handling better than stock. BTW I've never driven a slash so I can't compare.