Rear crossover pipe????

Well the oil filter is on that side as well so your most likely going to want to move that. 4" pipe is a good sized pipe and to be honest is just overkill. Its not needed. You can make the power with 3" and have a little more room for fitting pipe. Not familar with the magnum headers even thow I owned a dakota for some time. Is your cross over going connect to the headers normal ball and socket? Then you'll weld the turbo flange on the top? It may make changing plug a little difficult also if the turbo is right next to the valvecover. Youll just have to play with placement.