I might start lookin' at a early 70's Chevelle. The track wasn't real wide so it should be pretty close to the Cad, it's a Chevy, so parts will be easy to find and they had a V8 in them so should have pretty good frame integrity and sufficient strength in the control arms and such and disc brakes are a bolt-on. They were not rack and pinion cars, but I'm sure there are several sources for quick ratio steering boxes and other parts such as bigger brakes, sway bars, etc., etc. The rears were a triangulated four-link design and it doesn't get much better than that unless you want to hock the farm for IRS. Take a tape measure and head for the boneyard.