I've successfully built LOS from source!: https://lisalist2.com/index.php/topic,644.0.html
BTW, on the 2/5 wiring harness there is an unused 3 pin connector with +5V, +12V, and Ground available to use for powering drives as well.
I wondered the same thing. On my late 2/5, with an original Apple supply, I found only +12v at the connector. If it would have had +5v I'd have used it instead of the floppy supply.