If you found a good running 5.9, it may be cheaper than rebuilding the 318. Does the 318 need just a simple re-ring kit, or will the crank need turned, heads replaced, etc. You may not know the correct answer till the 318 is tore down. I do know good running 5.9 magnums can be bought between 250-350 bucks. Again, either choice is a good one. Or maybe we throw in the 3rd choice.... find a good used 5.2 magnum to replace the one you already have.