I thought it might be helpful to others to relate how I did this installation.

Sunday afternoon I started to tackle this job. I wasn't sure how to deal with the amplifier when I started. I ended up deleting it from the system.
I took out the old radio(remove glove compartment and cover plates to left of radio) and disconnected the old connectors from it. I used my meter to find the appropriate power connections on the rectangular plug.
Green wire was always hot, so it was memory.
Yellow/black was keyed hot wire.
Black was ground.
I wasn't worried about power antenna lead.

I traced the wires to the amp down to the bottom of the console, and proceeded to take the front off the console, and then the frame that held the heater controls. Then I could get to the plugs on top of the amp, which I disconnected.
My Bently manual showed which wire on the rectangular amp plug went to which speaker. I cut them and rerouted these speaker wires up to radio opening.

I left the plugs off the amp, taped them up, and closed up the console. Now it was the task of soldering the new radio's wires to the power connections and the speaker connections.

Took me a few hours, because I check, and recheck. Also takes some time to disassemble and reassemble the console.

I liked doing it this way, rather than trust in someone else's wiring harness. I don't know how they would have dealt with the speaker connections from the amp any differently.