Never get too hasty! I waited to install the PSU until today, and now I can confirm it is working flawlessly. Very neat and completely silent.
I planned to use the case and cables from an old C64 PSU, but unfortunately the inners were heavily glued to the case. At least I borrowed the cables from that PSU.
I wanted to use the power button and C64 power connector in the MB6582, so I had to patch the mainboard a little. It now works perfectly. I installed the 7809 on the mainboard, so that it will not use power while the machine is turned off.
All I need now is a neat case for the PSU. I've seen a few options at the bay, but have not yet picked one.