You might want to start by looking under the hood of a Hemi to get a visual cue of what looks different. I'm not familiar at all with what it looks like under the hood of a WK, but if you look at other models, not many engine accessories are a direct swap with different engines.
Then start cross referencing part numbers for the V6 and Hemi models for everything under the hood (power steering pump, radiator, intake, etc.) and find out what the differences are. I'm sure the size of the radiator will be the same -- but will the coolant hoses match up? Don't forget that all the electronics/wiring will likely be different, too. Everything will probably ultimately bolt in, but due to the size of the Hemi, I wouldn't be surprised if enough stuff is different to where getting a donor WK would be the easiest option to perform the swap. Sure you could probably find a wrecked WK and do the swap, but unless you are swapping engines just for the sake of doing it yourself, you may find it cheaper and even easier to just trade/sell what you have and get a Hemi version.
As for the acceleration of Hemi vs. 5.9L...who cares? The OP will find more than enough power out of the Hemi for his application. If he really cares about acceleration, he might as well find a way to put in a Gen III/IV GM V8 (LS1, LS2, LS7, LQ9, etc.).
Oh an another thing to consider is that IIRC in my state, it's illegal for 96 and later vehicles (at least without jumping through hoops) to swap in an engine older than the vehicle.
