Exhaust Manifold Application Question

they are both 318 manifolds. you will be cutting the flow of exhaust down with the smaller 318 maniflods on that engine. you should find some real 340 manifolds which have the bigger runners and have a larger dump on the end. the main difference is the flange on the ends are bigger. they will dump in the same locations. i just changed my 318 manifolds on my wifes car to the 340 hi-po manifolds and it fit fine. the engine on the driverside had to be pushed over some to get it in but it fit fine after that.