exhaust pipe diameter for a mildly modified 340

Stupid!? no way... This is the exhaust i want...

That doesn't sound like a old pickup though. I remember watching those videos. That's like a Commando single exhaust. But if I remember right, that's not the "Hemi style muffler" and no resonator. Sounds great and he really get's after it at about 28 min. Downshift and go. And then at 30 min.