On a 3" rear spring relocation is there a way to have tailpipes that will exit ± the stock location - or is the only option to exit in front of the rear wheels?

67 only had a single pipe running on the drivers side even on a dual exhaust system , the right side pipe cam over the axle and behind the axle . This was done in part because of the strap arrangement holding in the fuel tank and the J bolt in the rail on the right side . You can put duals on it by trimming the j bolt down after you hang the tank, Stock location on an A body 68 up was basically under the frame rail , a little to the inside , your problem is the springs moved inboard to the rails.

Where is your fuel tank mounted ?

Stock location won't happen since the shackle is mounted in the same location as the stock tip hanger, you can go inside or outside the leaf or go chevy II style and exit behind the wheels.

One of my friends has full 2 1/2" tailpipes on a narrow A with the leafs moved in and a stock gas tank so it is possible.

67 GTS 383 cars had dual exhaust and all big block A-Bodies had 1-7/8" tail pipes to get around the gas tank. No way to put in bigger without modifications. I have NOS 67 dual exhaust and they are 1-7/8" and do fit with the factory gas tank and chrome tips. I have done it on a spring relocated car by bringing the pipes between the frame rails and springs. A competent exhaust shop should be able to do it.