Thanks again for the assist ...
The good news is that I won't have to bother with reversing the modifications as I've spoken with the seller finally and he's already refunded the money; I'm putting the amp in the mail tomorrow to be returned to him.
I'm so relieved.
FWIW ... I found this 600LE amplifier (whacked out mods and all) to be far better sounding (for my tastes) than was my recently sold 323S and specifically with my 404LE's ... better bass, super sweet highs and overall just a more lively, and engaging listen; it's certainly a far different sound than was the 323S, which I didn't dislike but which, in retrospect, seemed a bit thin/cold compared to the 600LE.
So if anything, I'm happy to have heard a tube based electrostatic amplifier as it's given me some more food for thought regarding my passing, recent desire to go back to a dynamic set up. I might look for another (stock!) 600LE in the near future or perhaps one of the other Stax tube amps.