When I got the camera assembled back together, I tested the focus and the sensor for dust spots. Turns out that for hobbyist purposes, you don't need a clean room for the sensor assembly :)
Below is a shot of a gray roof, contrast enhanced, aperture priority @ f/10 (minimum of C-2040):
I shot several pictures and there were just three very faint dust particles staying in the same places. So not exactly perfect, but the spots are neglible in normal situations. I assembled the camera in a normal workroom and cleaned the sensor filter with soft paper cloth pads, some isopropyl alcohol and a blower.
The C-2040 got a bit near-sighted in the conversion process, I feel that landscape images aren't as sharp as they could be. Probably it can't get the focus all the way to "infinity". It sure gets it close enough, which is fine for me.
Macro abilities of course benefitted from the near-sightness; here are some test pictures, on the sharpest ones are laid 100% crops of different focus distance pictures.
Unmodded C-2040 has a minimum focusing distance of 80 cm and in macro mode its 20 cm. Converted has a minimum of about 25 cm, and in macro mode about 10 cm.
The new IR-pass filter of course hasn't got any coatings, so I was afraid it could add some internal reflections.. and so it did. Insane flare! So much for photographing something with point light sources in it :) The multi-coatings of lenses and filters sure aren't there for nothing;