I installed the M104 clutch successfully in 500E so I can share some info. The clutch I used is original and German made Behr clutch:
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Fan - due to different bolt pattern (M104 used 3 bolts vs. M119 clutch uses 4 bolts) fan needs to be replaced. I was thinking about fabricating some kind of adapter plate using CNC and keep using the original magnesium fan but gave up on that. My first attempt was fan from 2.1D Sprinter - these are widely available and supercheap in Europe. Part number is 1032000423 but it turned out that it is smaller in diameter, not much, maybe 5mm but I didn't like it. I also didn't like the colour but this is very minor... Next I turned my attention to V8 powered ML truck fan - bingo! Fan part number 11320000223 is a perfect match. I got it almost for free ($15) and in perfect condition - part is widely available here. It has identical diameter, same shape of fins and it's black instead of yellow:
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Installation is almost P&P. If your car originally had OE (thick) clutch it is necessary either to shorten the original bolt or purchase the new bolt from the hardware store as new clutch is "skinny" type. In my case bolt was already shortened as PO installed crappy Meyle part - no wonder that the car sounded like taking off Jumbo Jet when accelerating;
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If you decide to shorten the original bolt you will have to use a spacer (washer) between bolt and the clutch - the non-threaded part of the bolt is just little bit too long for the new clutch. In my case use of 2 washers was enough, they formed 3mm spacer. I found these in Porsche parts stash, perfect fit, no play at all, very tight, just like they would be made for this application

See below the original bolt shortened and spacer (washer) next to it - smaller one, the big washer was not used.
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After installation the new assembly sits 5mm closer to the engine than the original fan. I wanted to use another spacer (2mm thick) to move it away but decided it didn't matter and wasn't necessary. Fit is perfect with regards to fan shroud and other elements in front of the engine. I run the engine twice for some time and it behaves just like a proper clutch I think - car is still on Quick Jack so no road test yet. It's night and day compared to Meyle in terms of sound. Installed:
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