I just got a *new* 78 K5. Without taking off the differential covers or messing with the tires on a lift, how do I determine whether or not it has any kind of limited slip functionality? I remember someone telling me my old 77 had it, but I'm not sure that was entirely accurate...

 

I guess you could spin the tires on some gravel and then check to see if both tires had traction.
Personally, I'd remove the diff cover and inspect it, that is also a good excuse to change the diff oil for maintenance reasons.