jebediah
I didn't notice the cage measurements before, cage is a bit on the narrow side.
As Dylan mentioned, Zebras can get aggressive and protective of their nests. However, from what I understand, you have two males and not nesting or breeding.
You could give it a try with two male Socies, but I would have an extra cage on the side, just in case...
Everything depends on the individual personality of the birds. Some Zebras are milder than others, some more aggressive. You know your birds best and what they're like. Adding fake greenery and creating little private hiding places and corners might help if you decide to get the Socies.
Just my opinion.
~Elana~