I have no problem with the 3/16 mod. I did an ecu reset and havent had any problems with spiking. But others have so have a boost guage if you're gonna do it. What I did was seal off the snorkus where it meets the resonator. It looks stock and doesn't pull in hot air from the radiator.
You can gut the up-pipe easily but the downpipe is a different story. You have to cut it in half to gut it, then weld it back together. In the end you'll end up spending as much as buying a cheap dp.