Are the bolts rusted in or stripped in?
If stripped in, drilling/retaping or cutting the nuts off is the only
solution. There is no hope of removal otherwise.
If the bolts are rusted in, try enough heat to get the nut ( don't heat the
bolt and try not to over heat the tin cage) dull red hot. Use vise grips to
grab what is left ( either end) of the bolt and twist out.
I have has success removing bolts in through holes by drilling a 1/8 hole on
center, using a torch flame running through the hole to heat the bolt red hot.
Allow it to cool, then try to twist out. With blind holes this method won't
work so well.
How strong are the tin cages for the captive nuts? If they are thin, they
might not survive much torque.
The _only_ bolt extractor to use is made by Rigid, all others will fail. It
they don't fail, the bolt could have been removed by careful use of a center
punch to spin the bolt. These are a short straight spline with a internally
splined nut. The straight spline does not expand the bolt and allows CW and
CCW rotation. Sometimes turning a bolt a slight bit in one direction then in
he other repeatedly, breaks the rust allowing the bolt to come out.