Why not the super common swap to a Vortec 4.3? There's little aftermarket support for the 3.0 for mods and the power is down compared to the 4.3. Plus there's complete swap kits available. Not to mention trans compatibility and transfer case problems because of the pass drop axle.
But to answer the 3.0 swap question, engine harness, trans harness, PCM, custom tuning to eliminate the security system, some sort of adaptor to the Sammi tcase because Rangers are driver side drop and Sami's are passenger drop. Or divorced case, but then you run into a super super short rear shaft. There may be others but that's a good start.
Bottom line, 4.3 swap is common and cheap for a reason. Do it.
'01 XLT disguised as a '03 Fx4 Level II
Big. Loud. Slow. Bright.