Only use the Whopper with the fufnik linkage. If you are not planning on that, stay with the Big Mac. 63" Pro Comps will fit with only slight modifications. Remove that big U shaped rod, it goes from one front wheel to the other. Not sure what it does, but it's not needed. While you are down there with the front end off, you ARE installing the solid front axle right, cut those long bars that are behind each wheel. A 6" cut is recommended. Pro Comps fit with no problem. Looks great in the mall parking lots. Curbs and speed bumps are no longer a problem. Shopping carts crumble with ease.
Enjoy.