I'm thinking there's going to be a huge difference in wheelbase and it will look like crap. Now you could just go with a 3.3 chassis and it should line up better. There's a plain 3.3 chassis that's brand new in the classified section, as well as a really sick brand new carbon fiber chassis. I'm also going to have a really sick brand new custom airbrushed body (crowd pleazer 2 I think) that will be for sale soon, and it will fit the 2.5 chassis. I think that bodies look awful when the wheels are not centered under the wheelwells, and i think there are better options if you want to keep the short chassis. If you want to extend it, my Vantage chassis comes with the extended chassis, under armor, and center CVD's so it's a bolt on without having to buy the other parts seperate.
Rob knows the revos much better than I do, and I don't know how close the extended arms will put the wheels under the wheelwells, but if it's not just about exactly the same length I think it's going to look goofy.