I had all the same headaches as you, albeit with a different parts.
02 blazer 2 door 2wd, I lowered the front with 0.5" upper TBJ and 0.5" lower TBJ, Z87 springs (Blazer Xtreme oem, 1.5" drop), 2" belltech 2102 spindles, Spohn upper control arms and stock lower arms. When I was done and took it to an alignment shop, my castor was at 9 degrees with 0 degree camber, If I was at -2deg camber like you, I'm sure my castor would have been around the 12 degree or more you are seeing. I wasn't comfortable with it, and I had another set of used UMI arms (the non adjustable ones) so I swapped them in. With the UMI arms (which are sold with the 0.5" TBJ option) my alignment guy was able to get me down to 1/8deg negative camber, and 6.5/7.0 positive camber. I would have liked to have a little more negative camber, but I also don't want to be over 7 deg of castor.
So I would agree with everyone else's thinking that they companies are just recycling the G body stuff for S10s without realizing we have different castor outcomes. Sorry this doesn't solve your issue but at least you know you're not the only one with the issue.