Hi
I do not have the schematic for the 3-channel-dual-recto but I think that the LM Chip is for the stabilization of the DC-voltage -6,3V - you need to heat the preamp tubes. You do not really need to head all 12AX7 with DC. But most head V1 with DC to reduce interferences. So the chip is not really necessary.
Did you see other (older) schematics from the 2-channel-version of the amp. There you will see other opportunities to create the direct voltage needed for V1.
There you will also see that mesa used for all switches LDR`s. So I would use some kind of optocoupler for all switches. For some MOSFET Transistors should also work.
I hope I could help you a little bit. In these Forum are some other cuys they are much more familar with these recto amp than me - but I think they are afraid to write in english.
Bye the way - sorry for my english
Bye