Magnum exhaust manifolds

My 87 Ramcharger exhaust is on it's last legs and I was thinking of putting duals on from the manifolds back. I do know that 93 Ramchargers had the Magnum engines W/ the manifolds. They are supposed to flow better than the LA type manifolds and i figure that maybe I can pick up a few HP and milage by swapping them out. Are all the Magnum manifolds the same (other than outlet size)? Would the swap be worth the aggervation, work, expense etc... Should I forego the manifolds, install headers (long tube or tight tube) or run the duals from the stock manifolds?
This is a stock 87 Ramcharger 4wd, 318 2bbl. I am trying to make it get the best power and milage I can out of a bone stock truck.
Thanks!