You have manual and automatic hubs in that vintage truck, see:
http://www.off-road.com/toyota/tech/aisin/

If you can find someone with automatic hubs, you can probably make a trade for your manual hubs, since most folks with the automatics want to get rid of them

It would be a fair amount of work to retrofit the automatic differential disconnect into the early truck. With the manual hubs, there is no rule that says you must always unlock them after use. Some folks I know who live in snow country, lock their hubs at the first snow and leave them locked until it melts in the spring. Then you just shift in and out of 4WD as needed with the transfer case shifter.