Problem solved!

it was a little more complicated than i initially thought. It seems that the brazed on IS disc tab was a little off. I had kind of come to that conclusion myself but didn't think it'd be the case.

It also seems that this sort of thing happens pretty regularly. There are even alignment tools for it! so i suppose the bike manufacturers kind of let the disc tabs slide.

I took it down to my LBS and they fixed it up right for me for $20. In the end they had to take about 1mm of paint/metal off of the inside of the tab and then work it with a file for a bit. Fits like it's supposed to now and the brake mounts perfectly.