For whatever its worth, the later versions of the 5.9 compared to the later versions of a 5.2 doesn't impress me much. The Magnum was designed as a 5.2, but opened it up to a 5.9 to sound more impressive. The difference between those two does not compare like the difference between the LA 318 and the LA 360. The 360 LA motors had heads with bigger ports, larger valves, and a block with a longer stroke and a bigger cam then the 318 LA version. From what I've read, the Magnums have the same heads, same block, and nearly the same cam profile. The magnum 5.2 has nearly the same output as the 360 LA.

As far as the pictured Dakota, locate a V8 truck for parts, everything should bolt up, and you have the wire harness if you need it (throttle body = probably not, switching to port injection = probably yes). Differences being motor mounts (at least the part bolted to the frame), radiator, possible wiring, computer (V6 to V8), and odds & ends.