The HV is around 1.2kV, 6kV and a switched supply of +- 2kV. I have some old HP laser boards with these blocks on them. The filter is mostly to remove the off axis scattering, as the drum will otherwise have a broader spot on it.
The laser is only on a heatsink, and has a feedback diode on it as well to control brightness. Invisible IR beam, you would probably want to replace it with a red led to see it, though this will destroy the alignment for precision work, but good enough to just power it and turn the mirror to show the beam moving and being corrected by the output lenses. The HP optical blocks i have seen have another folded optical path in them to get a broad beam in a very thin box.