tail pipe

I installed TTI headers and their 3inch duals, onto my 68 Barracuda(360/4spd). The rear end was narrowed, and the springs moved inboard with the offset kit. This to fit 325/50-15s inside the factory tubs. The car was lowered a bit so the wheels are actually in the tubs, but just barely.
The fueltank is a stocker, and the TTI tailpipes thread the needle just right. But
forget about the factory tips which IIRC fit on 1.875 pipes.
I ordered my 3"TTIs with 3"turn-downs.

If you are looking for the 340 sound, you need the whole enchilada; that is to say; the 10.5compression 340, log manifolds with working heat-riser, the 340 cam, the small pipes, 3-pass walker-type mufflers ,and of course the tips.
If your 340 has an aftermarket cam and headers, then the growley 340 sound is pretty much gone, anyway.