I replaced the drivers for X and Y axis with SilentStepSticks from Watterott. They come with heat sinks that are higher than those on the stock driver modules inhibiting mounting the original top-blower again.
Since the top-blower was of not much use anyway (it's blocked by the bottom sheet metal which has no openings in place there) it was time to design this fan holder.
The fan holder can be mounted with the screws of the old metal holder, but I used the longer screws that held the old fan. The holder should also be glued onto the "ceiling" using double-sided tape to avoid vibrations.
You can use the old fan, or two silent ones (50x50x10 mm). If you want to mount two fans, you have to solder or use a Y-cable, of course. And your replacement fan must have mounting holes with 40mm distance (I've seen ones having 42 mm).
I ended up fixing the fans using those - um - silicon straps that were left-over from the Noctua fan I use as the nozzle cooler. That way no vibration is transferred to the chassis at all.
Note: The place for the M3 hex nut is designed with 5.5 mm distance which should be enough in theory. However, mine came out too small to actually insert an M3 nut.