FWIW, I'd use manifolds off a 90's 5.9 Magnum engine - 318 is the same also I believe. They are a great design, & bolt right up. I pulled the crappy manifolds off my 73 340 Charger Rallye & used Magnum manifolds w/no gasket. Only thing I had to do was get a different trans dipstick tube from Masta Performance - the RH OE tube was in the way of the manifold. Everything installed from the top no problem.