I can say without hesitation that my swap was a complete pain in the balls compared to anything I've ever done. Granted, I went through top to bottom, replacing every seal, sensor, camshaft adjuster pads, t-belt, bufkin, turbos, fuel pump. We have a very well equipped shop and it was still time consuming. As long as you enter into the project with that understanding you should be fine.

And definitely plan to go over budget on unforeseen parts!

Just for comparison, my buddy installed an RK supercharger and twin disk in his e39 M5 in about two days, taking his time!