You did notice that they say that one is for oval track racing only, didn't you. It really isn't that bad. Just heavy and tedious. You'll need a couple of specialized tools, a shop press, and having a friend around helps a lot. I use the crush sleeve eliminator kits instead of a crush sleeve, and it make things a lot easier. Also, change out your bearings and sleeves while your in there. It's not something you want to get into often.
I swapped out the open diff in the 8.8 rear end on my F150 for an Eaton posi, and it wasn't as bad as I feared. I reused the 3.55 ring and pinion, but went with new bearings and seals. Mark you diff caps, before removing and keep everything organized, and it's not that bad. The nearby autoshop wanted $60 to press off the pinion bearing, another $60 to press the carrier bearings on, and another $60 to press on the pinion bearing. I went to Harbor Frieght and now have my own shop press. Cost $200 and now can use it whenever I want. The 12T press would have worked fine for what I did, but I got the 20T, cuz it was on sale. A lot of shops will do it for 10 bucks or so, but I think the one I used to visit, just didn't want to bother.
Anyway, it's not that difficult and I disagree with those who say a normal DIYer can't do this. Just don't rush, take your time, and if you run into problems post up some pictures and someone here should be able to give you some pointers.
Good luck!