cats the bulge in the dp under the car, id not get a high flow cat. your car will likely set a cat code with it.

your car na or sc? how many miles? na engines tend to clog the cat much more often.

no idea on the ticking, we would need to hear it. so take and post a vid if you can.

if there was no dents in the plug ive seen them shut the gap on their own. if it looked smashed you just might have a chipped piston.