Welcome to the place. I used to have an M3-Blond. Great organ.
The speaker jacks are wired in parallel, so use either one with your 8 ohm cabinet.
As for schematics, if you remove the chassis you will find a number etched into each circuit board in the amp, like PC5065. Post all of the ones that you need and we'll see if we have them to send you.
What is wrong with the amp? Is it humming? Why do you want to replace the filter caps?