There were several different keg manufacturers and even different models from the same manufacturer, so there are several variations for the post threading. You can't find any other identifying marks on the keg at all? You're sure it says spartanburg and not just spartan? The ones you bought look like they're for the newer firestone kegs (9/16"-18 tpi for the gas and 5/8"-18 tpi for the liquid). You could have a cornelius spartan which needs 19/32"-18 tpi for both. You might find this helpful-
Just out of curiosity, what's wrong with the original posts that you're replacing them? It's very uncommon for the post itself to become damaged enough to need replacement. They usually just need new o-rings and sometimes new poppets.