Yes it could be to rusty to fit a nutsert but if it looks solid and you dont want to cut it apart and want to get it running again it could be a solution.
We fit them up to 12mm at work and they are extremelly solid
Look at 365days project he has fitted them to his front subframe to mount the guards.
i can send you some free of charge to try its just the guns worth 2500 dollars but you can fit them by using a bolt and washer to pull them in.
http://www.youtube.com/watch?v=eWAStq241ug&feature=relatedPete