Any problems putting 3’ exhaust on 70 Dart ?

@toolmanmike, no one slammed you against a wall. For what it’s worth I’ve done a lot testing on turbo stuff with back pressure because it relates directly to the AR of the turbine side. I logged exhaust pressure pre turbo on my daily driver and every time backpressure goes down and all other factors remained the same, power went up. And any restriction at all, after the turbo causes it’s own problems. Backpressure anywhere In the system is bad. This is not race car stuff. It’s street car stuff also.
Sure, I shouldn't have used the word backpressure if it's getting the experts here all jacked up. Plain and simple, the OP probably wouldn't notice a increase of performance in a 3" system v/s a 2 1/2" system other than the cool factor and a little difference in sound. I don't think a 3" system is necessary unless maybe you stick a 505 stroker in and you probably shouldn't be running it on the street anyway. That's my opinion and I'm entitled to that.