Technical input that might be of interest, though not providing exactly what Greg requested. This from my bro-in-law who is a talented musician (keyboards his forte) and studio owner (engineering, production, mastering). He’s in the AllMusic Guide for what that is worth. He owns a couple of Hammonds including a B3 that he refurbished. Safe to say he’s intimately familiar with how they work. His comments:
"Key click" and "percussion" are two different things. They are commonly confused with one another.
Key click was the result of an electrical contact being made when a note is depressed on the organ. Key click was considered a flaw and Hammond used frequency filtering to help suppress this.
There are ways to accentuate the key click by tapping directly out of the organ’s preamp and going straight into a mixing console or guitar amp. Organists like Keith Emerson, Jon Lord and many others utilized this sound.
Percussion was a design feature that was introduced in 1955 on the B3 and C3 models and then later it was available on most other models. The percussion effect is a set of four tabs on the top right of the console that when depressed, adds varying degrees of harmonic attack to the note. Sort of like when you strike a marimba or vibraphone. It is in no way like the sound of key click.