Truck manifolds are bigger than car manifolds. FE engines (truck) from 65 through when Ford stopped making them use the same manifolds. Likley Ford sells them. Truck manifolds flow pretty well for just driving around. Headders are great for race cars but are a real PITA when it comes to leaks and cooked starters. So if you are just driving your truck, manifolds are fine. Be sure they are flat and true (machine shop) and add a set of gaskets. Follow torque sequence and specifications. True duals with a crossover pipe or even a X pipe if you want to spend a few bucks. Not interested in re-starting the age old pi$$ing contest about headders verses manifolds. This is my opinion based on 50 years experience working on these old trucks. IMHO!