A tonewheel organ could be amplified acoustically, e.g. by physically touching an appropriately sized resonant chamber to the wheel when you press a key. The exact size of the resonator does not matter because it's mode locked to the wheel, which turns at a speed determined only by the gear train. Tonewheel organ gears traditionally do not have perfectly accurate tuning, but there's no reason they couldn't be built to match any tuning system within the limits of human hearing (at greater cost and complexity).