soak the bolt heads with penetrating lubricant for a few days if worried
work slow be patient
I have never had broken bolts on oldies so you may have no problems.
you can try a freeze spray to break the bond or heat the bolt heads if they can be reached and apply a release agent so the capillary effect can allow some to penetrate. Clear as water silicones seems to work ok.
sometimes a 1/4 inch impact driver going clock wise for a short burst then CCW may break the bond but don't overdo it. go manual if worried
