A vacuum shift axle is a lot smoother shifting and somewhat easier to use than the electric models. With a couple of solenoid valves and some creative plumbing most of the mechanical bits and pieces of the vacuum shift system can be upgraded to electric switching and the original vacuum shift rear end can be retained. A 2 position toggle switch on the shifter makes shifting the axle easier, and the vacuum axle has a lot fewer parts to fail in the shift system.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!