I highly recommend the LCM.
Any modern power supply will be safer and more reliable. If there's any doubt about the pinout and cabling arrangement of the old power supplies, it's totally possible to pull the old power supply, repair it as best as possible with new capacitors, power it up on a test bench and probe it to see exactly what its output is. Then match that on a new cable harness with a new power supply.
It's not "hacking" to provide +15V or -15V , that's within the range of many good quality tunable 12V power supplies.
Some of them even come in specific 15V versions like a Meanwell RSP-750-15:
You could easily get the impression that electrolytics had really lousy lifespans as a result of this.
Not a single one built after 1999.
 Complete schematics at http://bitsavers.org/pdf/xerox/alto/schematics
 Source code at http://www.computerhistory.org/atchm/xerox-alto-source-code/
 Simulator at https://github.com/brainsqueezer/salto_simulator