Bob,
That's great! The old Hammonds have some good, innovative stuff in them. The transformers are often re-purposed for use in tube theremins and custom amps. And the leslies are still popular. Hammond and Leslie both used mechanical rotation - the organs had a "tone wheel" used in the generation of the notes. The Leslie had some of its speakers mounted at the ends of a rotating arm. The speed could be changed to create anything from a deep, slow "spectra tone" to a rich, lush vibrato. But the leslie speaker cabinet also housed a variety of speakers in contrasting sizes, mounted in casework of good material and generous size. All-in-all, the overall tonal effect was good enough to make these systems very popular.
I strongly believe in re-purposing and recycling. It can be downright fun to combine the old and the new, as surprises happen along the way. But I also respect the ability to make new things all from scratch. Some of you can do that with circuitry, down to building your own effects or whole complexes of inter-related circuits. I know that some of you people post on this website, and I have nothing but admiration for your experience and abilities. And there are others who possess a different form of "genius" - the ability to integrate the old and the new to achieve a pleasing end result. Hats off to you, too!
Even though the 12" speakers will require larger-scale cabinetry to mount (thus limiting how "compact" you can make your casework), they add considerably to both the low end of your sound and its richness overall. The little 4" help the high end, if they are used just lightly (they can sound tinny/screechy if overused). I find that the speakers are one of the main factors which determine the minimum size of the instrument. But since we are purposely building a self-contained system, portability takes a back seat to sound-quality and function. We are deliberately building an all-in-one, and we want to put enough into it so that in the end we will be pleased with its performance, without having to use externals. Sure, we can still cable into larger amps, sound systems and effects, but we don't HAVE to use externals to sound good....That is the main purpose of a self-contained system. So we might as well NOT skimp on size, just to save weight. We will probably keep these instruments in our homes and studios, most of the time, even as we travel about with our portables.
On my current build, I'm incorporating a Boss harmonizer as well as the Electro-Harmonix talking machine and the Holy Grail reverb. I gutted the harmonizer and moved the circuitry up to just under the Moog Etherwave Plus. I've mounted the talking machine and the reverb in that same vicinity, so that all of my controls are all conveniently located. I have added leads to the circuit boards which run to my video sockets, for the hand controller glove. The reverb case with its latching foot switch is mounted next to my volume pedal, but the circuitry has been moved, as described above. Generally I dislike the foot switches which are still being used on pedal effects - they are VERY noisy! So I will rarely make use of the reverb footswitch. I can simply adjust the amount of reverb at the knobs - clear down to zero. Like you said in your post, these effect units can be modified in various ways to serve our purposes, and we can do so without having to "re-invent the wheel".
Keep me posted. I'm interested in your work.
Will be posting pictures in a week or so.
Jon