This is actually a pretty easy thing to do IF YOU ARE NOT A PUREST.  Take the large size, rear dump exhaust manifolds from '57 or later pass cars and swap them side for side.  They will then dump near the front of the engine, so you will need to have pipes fabricated to curve down and run under the rear motor mounts on the bell housing, then to the mufflers of your choice.  In Dyno testing a few years ago the later pass car and the rams horns did just about as well for power and torque and of course this eliminates any problems with the clutch.  I believe this trick will work for all pickups but it is easy to try.  You can also use two right sides so the passenger side dumps to the rear and the driver's side dumps to the front.
doug is 50% to doing the dual easey,use the large size dual on the right(pas side) use the single  pasenger side on the left ,block off the port wher crosover went then get a preformed piece and it will be easey from there and will look ok the one i did the header pipe bolted richt to the pasenger  side dual type manifold.the custom made pipe on the left willbe easey and you will have a tideyer drivers side ex than the rams horn