Couple of comments about the Spicer hubs.
I see everywhere that they will fail in the locked position.
Not necessarily.
I had the Ford version on my '79. Had just gotten it out of the dealer shop on Friday for some warranty work, and they had repacked my front bearings while they were at it.
Saturday morning, I was going mullet fishing. (Its a fish, not a haircut).
Normally I can drive all over crooked island in 2wd. This time I hit a soft patch of sand and started digging.
Hopped out to turn the hubs.
Left hub would not turn. Totally locked in free. Tried pliers, no luck.
Normally I would have some Allen wrenches, but had used them for something else.
Nothing to winch to. Plus I was facing the sound, did not want to winch myself into the water.
It was a long walk back to the mainland, or a 1/4 mile swim across crooked island sound.
Didn't really want to do either.
Found a nail in a piece of wood floated up, and used a hammer and my big front bumper to pound it into a semblance of an Allen wrench and got the screws out.
The outside bearing nut had backed off to the point that it was rubbing on the locking hub. That generated enough heat that the two arms melted into the plastic actuator.
Not far enough to engage it, but far enough that you could not turn the plastic part.
I got it engaged and the heck out of there.
Also, if you use a Ford one, not sure of the general Spicers, but those have a tapered spring.
DO NOT go by the manual which says put the small end towards the bearing.
If you do, the big end will drag on the splines inside the hub, and not be strong enough to push the locking part out every time.
Found that one out the hard way too.
there is NO wheels bearings in that hot burnt up mess. 
