I think the thing to try is a low-buck "port-match" of the factory manifold followed by a trip to the "Extrude Hone" folks. That will max out the flow of the factory manifolds yet retain a factory look and keep the costs down. This process works really well on "resto-mod" muscle cars. It avoids all the cost/fit/noise/leaks issues associated with headers. A decent factory manifold moded in this fashion will make almost as much power as a set of headers. The headers don't really show much gain until high RPMs very close to red-line. There are some exceptions; some engines have just horrible factory manifolds. The M-Benz 3.2 set look pretty decent !

Slim