You may already know some or all of the following:

1. The bolt "ears" on a Fenton exhaust headers do not match the thichness of the stock ears. I think you will have to grind down the ears on the Fentons to match the ears on the intake manifold (stock or other).

2. There is a heating outlet hole on each header (2 holes, total) and these will have to be plugged (brass or steel plug). Later on you can decide if you want to use these holes for a source of hot air to warm the intake manifold.

3. You will have to separate the stock intake manifold from the stock exhaust manifold (these bolts do not loosen easily). Will you be using the stock intake manifold and carburetor?

Do you know if the stock intake manifold clears the Fenton headers (Fenton headers and Offenhauser intakes need to be adapted to work together)?

If you mean "off the shelf exhaust system", Jim Carter sells one (regular steel and no mufflers or clamps, $200).

Tim