I have seen people do double wide tracks, not sure how it is done exactly but I am sure there is somone who could point you to a tutorial.
Add side mounted armor plating cut from plasticard or bought from forge world or for historical models. There should be a tutorial for this on the GW websight.
You could use space marine predator turrets. Again there is a tutorial on the GW websight.
http://us.games-workshop.com/games/40k/imperialguard/painting/treadheads/p1/default.htm
Good Luck.