For the guys who have access to some machine tools, the Laycock overdrive that was used on Volvo, Jaguar, Austin-Healey, Triumph, and other European cars is exactly the same unit Gear Vendors is selling as an add-on overdrive. It's got a self-contained hydraulic pump driven from the output shaft of the transmission it bolts to, and it's possible to machine an input shaft that incorporates that cam, add an input flange, and make the Laycock unit a stand-alone, divorced overdrive similar to a transfer case. All it takes is an electric signal from a toggle switch to engage/disengage it. Those OD units are available on Ebay for pretty reasonable prices on a regular basis.
Jerry
