Either you've got some weird setup, or you don't have all the parts out yet.
Have you removed everything inside the hubs, and can see all the way down the splines to the bearings? The spindle and it's threads will be riding in the middle of all that, with the small splines end of the axle shaft sticking out of it's center.
You should be able to clearly see the outer nut with it's 4 notches.
The opening on a standard wheel hub is quite a bit larger than the 2" that you're talking about, so something seems amiss. What is the far-outside diameter of your hub? Should be roughly 3/16" thick material outside the outer splines. Roughly 3.25" outer diameter, therefore roughly a 2 3/4" to 2 7/8" inside the splines?
If not, you still have some digging to do. I know we run into '66 differences all the time, but "officially" anyway, your '66 uses the same stuff as they did all the way into the '80's and beyond.
Good luck.
Paul