Heat rises, better cooling would be achieved by reversing the flow of the fan from blowing on the LED array to pulling the hot air up and out of the top.

Another way would be to figure out what light wave length(s) variable contrast paper is most sensitive to, then pick LEDs that best match the VC paper sensitivity range, apply a light output controller to each color LED (wavelength of light), put the LED's light output into an integrating sphere with the light output of this sphere into the enlarger (similar to a single light bulb). This results in a variable contrast paper light source that is more efficient with a very high degree of VC paper contrast control.

Not a simple project any more,
Bernice