Why not simply copy the one circuit and place it in yours.
At the junction of R23/ R24. (remove the Ground connection)
The Fender circuit is slightly different as it is a fixed bias amp.
Yours is cathode biased.

It does not look as if the Tremolo is connected properly.
It "normally" feeds the bias of the output tubes.

Leave the Black Lead attached to chassis when taking voltage measurements.
The negative voltage can be read at R 63. (Red Lead)
The rectifier side should read -46Vdc and the other side has a zener diode (CR30) attached which will drop the voltage to -15Vdc.

Peavey schematic indicates Volts dc.

Thank you, Enzo.

China: https://www.ebay.com/i/223267113613?chn=ps&norover=1&mkevt=1&mkrid=711-213727-13078-0&mkcid=2&itemid=223267113613&targetid=4580771608074811&device=c&mktype=&googleloc=&poi=&campaignid=403204658&mkgroupid=1234751773358313&rlsatarget=pla-4580771608074811&abcId=9300377&merchantid=51291&msclkid=dabb26252d0c16366a5079ff850aac97

I cannot find a schematic for this model amp.
Do you have one?

What in the world is a 'Crate Gaza'?

The Selector switch is SPDT.
The rest are SPST.
All must latch.

That is a 6 pin male DIN plug.
The drawing of Pin #7 uses a flat line to indicate 'attached to shell'.
It's the braided shielding wire to ground.

Schematic & footswitch info: https://www.ssguitar.com/index.php?action=dlattach;topic=4374.0;attach=7781

Here is a pic of the switch.
I think you are going to be hard pressed finding a 5 button switch.
Do you need all of the functions?

Well I see that they highlighted the Reverb section.
So you can ignore the one op amp. (IC3)
I also see that it looks like the Gain control is snapped off.
If so, set the amp for Clean and look at the output pins of IC1 Pin 1 & 7.
I would think one output is for Clean & the other is for OD.
From there it should go to the relay.
The relay output should go the the LM1875/ Pin #1.
You do not have to have a scope.
A decent volt meter set to read Volts ac should suffice.

C23 looks as if it is a part of the Reverb circuit.
There has to be a separate input for the dry signal.
You show the tone control going to an opamp.
That may be it.
There is no label of the output pin. Pin #7?

You will have to trace out what is supplying the input signal to the LM1875.
Most probably one of the opamps.
Use the schematic that I attached to verify what input pin they are using. (Pin 1 or 2)
It should be a capacitor coupled input (C12?)
If so, you can lift that cap to isolate the LM from whatever is driving it.
(this may be called for if the LM is toast & dragging down your supply signal)