check this out
http://www.moparts.org/Tech/Archive/exhaust/9.html
theres some posts also on this issue
for the most part if you have p/s the drivers magnum manifold won't fit without a lot of grinding and frigging, non p/s seems to be ok even on the earlier a's
magnum passenger fit is easy
I have the 68-71 340 on the passenger and the magnum on the passenger
if you hunt around you should be able to pick up a 340 drivers manifold only for 75-100
there is only 7-11 horsepower difference between the 340 and 318 exhaust manifolds
