Ugh, I just had fun fixing that on my K25, lol
Basically, you'll need to back the bolt off as far as you can (or if you can get it out, do so!) using vice grips to try and hold the little nuts underneith there, then cut the top of the nut off so you can get the rad support plate off of there. Then, spot weld those little nuts down to the top of the core support, then use vice grips to try and get the cut bolts out, or, thread a nut on top, and then weld it on (get good penetration) and use an impact wrench to back it out.