You may want to search on "400E timing chain" and see what others have written about doing the job on that engine, since the M119 engine is used in both vehicles. I haven't done the job myself or seen it done, but I don't remember hearing about the cams having to come out. I have heard from one advanced DIY'er who did his own timing chain and upper rail replacement on a 400E in about 7-8 hours, and having done it once feels he could do it again in about 4 hours . . .
If the search doesn't yield the info you want, you might want to repost something like "Book time to do timing chain on M119 engine?" or "Cams need to be removed on M119 to replace timing chain?" or something like that which is equally specific.