Bosal seems to be on the same level as Walker, both make pretty decent OEM replacement stuff. From what I've heard, they both tend to be more on the quiet side, a well as tending to be smaller diameter (be sure to get matching diameter for the exhaust immediately before and after the midpipe to cut down on rasp). I temporarily had a Bosal muffler for a coupe in my possession (sent it back due to getting a Tanabe), and it seemed pretty well put together, although the pipe diameter was tiny and it would have needed a helluva buff and polish before going on the car.

For a midpipe, it would probably work, although I'd recommend finding a used, good condition coupe midpipe, as you'll know it'll fit for certain. Z1 sells new ones for $350, although at that price you're better off just getting a whole system.