On my new top case, the separator between the dvd drive and the motherboard was missing (the one you can see on the left of step 50 picture). Took the one from the old top case and it worked but I dont know if my new case was missing it or if something is missing in the guide.
Also the screw to adjust the "click" of the trackpad is a nightmare.. I dont know how I managed to make it work but I hope I ll never have to touch it again as I think it is a bit "screwed" now.
Except this ... everything went fine and I can now use my macbook like before which is the most important !. Now I feel more confortable, I may open it again to put a HDD instead of dvd player.