Have you considered the exhaust manifolds used on the early 1980's 305 engines, the ones that have a rear exit at around a 45 degree angle? With a little creative pipe bending by a good muffler shop, it's possible that your frame and steering system clearance issues could be solved that way. We used those manifolds on "claimer" race engines in a class that didn't allow headers, and until the RPM really got high, there was no appreciable loss of power compared to ram's horns. There's also a set of exhaust manifolds that have a 90 degree rear exit.
Jerry
