So how can you tell if the upper control arms have been switched from side to side?

hmmmm........'cause you're getting negative caster?

Oh....that was a question, not a riddle?

The upper ball joint should be closer to the rear than the front. If you look at the cont. arm from the top, you can see a definite "curve" to it, in relation to the ball joint. The "curve" should curve to the rear. The upper ball joint will be behind the lower ball joint, if you imagine a straight line up from the lower ball joint.
Don't know if this is clear, but I hope it helps.

Thanks Joel, that clears it up. I'm sure the arms are correctly installed now. Basically the short side of the upper arm is towards the rear. I have an issue where the tires (especially the right) have a slight rub on the lower part of the fender during lock to lock steering maneuvers. The alignment shop has about 3/4" of spacers on the rear control rod bolts, none on the front. I think that has pushed the wheels back farther then normal. Time to get to another alignment shop for a second opinion.

while installing my front control arm i noticed i had mixed up the upper one  although i thought i had keep side by side but somehow during the restoration process i had swapped them .  but it is quite easy to notice the difference , specially when you try to get the balljoints in the knuckle you can see the lower and upper are not in line

 

art-corvette

Nice pic!
If you swap the sides, the spindle would be almost straight up & down...........not good!
Thanx for the pic, art-corvette!