In the meantime I created a cased version of the illuminator as well.
I have reduced the number of LED modules to 2, and raise the current for maximum light output.
The LED modules are now driven by 1A, and instead of the old-school linear current regulator I used quality high efficiency switching regulators. The LEDs are the 850nm ones, again from Osram.
The total output light power is now ~8200mW, the IR module is just slightly warm after 1 minute of run, and as the full case is aluminium, it distributes the heat very well.
Because of the casing, the module can be hardly abused, without the fear of destroying the LEDs.
Now it can be mounted to ANY 250-sized quadcopter via a single velcro strap.
The input can be 4S only, a 3s LiPo does not provide enough voltage for the module.