Making a car sound
radical is easy. Just install some cam with at least 240 degrees of duration @ .050 that has 'plenty' of overlap, and hope to goodness your power brakes still work afterwards.
Making a car be
radical requires a lot of thought, effort, planning and lots of attention paid to the details: what transmission? what rear gear? how (and where) is it going to be driven "most of the time"?, what are the specs on the torque converter?, heads?, intake and carb?, exhaust?, what rpm range is it going to see most of the time? etc