Hi Chip,
Great stuff to add this overdrive possibility.
In the mean time I have advanced on cloning the entire KLM-368 board.
I am now cleaning up design rule violations on the board traces.
Since your overdrive is entirely acting on the KLM-368,
I was thinking of embedding your mod into my schema.
What you do is to control the input attenuation through an analogue voltage on P-Vol.
From my analogue eye, this may be possible in a more direct way through a couple of active elements, like transistors resistors, or maybe an LED-LDR combination? Will think about it.
Cheers,
Haitar