I think any smallish socket 370 or socket A heatsink would able to mount on the lugs around your socket 7. Just be careful not to wear them off.
Oh yeah, I ran a P1-133 fanless, with a stock heatsink not
attached by the lugs ('cause one of them broke), without thermal paste, for something like half a year and it worked fine with a small enhancement
. Perfectly stable and all. I don't know how long that could have kept on going, as I upgraded. I'm afraid your K6 is a lot hotter, though, so it's probably best not to try that.
As for power supplies, it's luck of the draw really. I had an old non-standard form-factor Compaq PSU with AT plugs and it was a lot quieter than most generic stock PSUs. Failing all else, the computer draws so little power that a fanswap with whatever SPCR's current 80 mm favourite fan is would be perfectly fine. Run it at at 5 V... and enjoy finding that the old hard drive makes noise, too