You'll be wanting moi.
I can't see any mods in the photos? Although some of that wiring could be new, looks stranded instead of solid core.
Yes you can use a 24V supply, the minimum transformer EHX used was 12-0-12 for 24 volts (ish, AC 'n' diode drops 'n' all) it's regulated through a zener/transistor capacitance multiplier set up I think on this unit but some did use a 78L15.
Schematic attached, it's not 100% accurate, been a while since I worked on this particular version but I recall that being the case, but close enough. I've replaced one SAD1024 in the past year, on EHX stuff, check the Op Amps First.