There's a locksmith on eBay that sells exactly what you need. I had him make keyed alike ignition and door locks for my 4 squares and my OBS. 1 key fits all 5. Every lock. When I bought the last one I messaged him about keying it the same and it was no problem.
ALL - The only 24V CUCV part is the starter. All others are 12V. Glow plugs, IP, relays, etc. All are 12V.
OP - The Roscommon method works very well. Also check out the Doghead relay mod. There is a starter relay under the dash that goes bad on almost all of them...