It seems like people that work on cars for a living always seem to think they know more about the kind of cars we are into. I have a 68 with a full 3" exhaust with 3 chamber flowmasters over the axle. The first place I took it to said the biggest pipe they could bend over the axle was 2.25", I did'nt even argue with the guy, I just left. I asked around for a more reputable shop and then found one that could do the job. As for a lowered car, my car is pretty low with 2" blocks in the back and lowered springs in the front, the rubber stoppers on the lower control arm are about 3/4 away from hitting the frame, so I think I need shorter stopers. Hope this helps, the 3" exhaust was a little expensive and it's pretty loud, but my car is a big block so I thought I should get the 3", if you're running a small block I would think 2.5" should be just fine.
68 468 700R4