Hey Mike,
The driver won't care where the power is coming from, so yea...the "donor" amp will work. Not sure about running it through the plate amp, I doubt it. You can take the amp off and make a wood cover plate with a hole to accept the new wires, or, drill a hole in the box and run new wires through it leaving the dead amp as the cover plate.
I've fixed some 'dead' amps by replacing the bad caps in them. Do a Google search for your model number with key words like 'dead', 'blown', etc.....
You might be able to fix the amp for less than $5-$10.
Bob