Just to clarify, the front axle engagement is done automatically. It kicks power to the front axle when any rear wheel begins to slip 6% faster than the front. The sprag which controls this action just needs to be told which way to deliver the power to the front axle. This is done via the "reverse shifter rod" on the front of the transfer. As said above, it is spring loaded and requires a decent amount of force to pull outwards out of it's ball detent. Out for "reverse" and in for "forward". With no linkage hooked up it is automatically retracted inwards via an internal spring.
Tburk, that is quite amusing that the previous owner used the idea I had. Tis a small world. I completely forgot, you are correct in that "forward" mode there's no need for air pressure. So it would be safe as well. I can only imagine how he hooked it up. It looks like a simple setup, atleast in my mind. Any chance of pictures, or a model number/make for the air cylinder? It would save me a lot of shopping and crunching numbers for power specs....
I love the idea of rigging the electricals to the Reverse gear on the transmission. It will be easy for me since Reverse is at the very top of the shift pattern. Park being utterly useless, it will not be used. Time to buy wheel chocks.