I saw a resto-mod website of a 48 Ford Business Coupe or some-such where the guy used 2.5" or 3" PVC plastic pipe and fittings to mock up his exhaust from the header flanges to the tailpipe. Once you did that, you could take the assembly to a muffler shop or order the bends and straight pieces to fab your own.
Plastic pipe is cheap and easy to work with, I thought that was a pretty good idea.
Just another data point, I think the replies on this so far are more on point.
