[BR3W CITY]

Both my old setup and my current setup run an exhaust thats at least partially outside the rails.
My old setup cross under the rails at the kick up in the wheelwell area, and then ran outside the frame all the way to my through-step exit.
My current setup runs inside the rails to the trans crossmember, then crosses over for the muffler mounts and the side exist.

A couple things I ran into;

Unless your starting with a dragster style header that actually exits over the rail, you have to cross over the frame somewhere. With a larger tube (unless you go oval), this can cost you some ground clearance.

It can be a bit hard to get a jack on the framerail if your exhaust tube hits first.