Magnum Exhaust Manifolds in an A Body
Heres the dyno tests on the manifolds
http://www.moparts.org/Tech/Archive/exhaust/9.html
As you can see there isnt much of a difference between the magnum and 340 manifolds.
I cant find it again but I saw a chasis dyno test on a 340 in a Duster which had mild "plus" engine and there was only 20 horsepower between the headers and the 340 and mag manifolds
Also have seen where a couple of guys have installed mag manifolds in a bodies with MANUAL steering where there was some massaging and grinding but had a sucessful install. I have NOT seen a manifold with power steering without there having been major frigging and grinding.