Heat then take a can of Air duster, turn upside down an freeze it , turn it out.....
It’s a busy thread. Thanks for following up to my replies.
Someone up-thread asked about backing strain on the bolts (e.g., two blocks of material bolted together.) If that’s the case, possible you could compress the fixture with clamps to relieve the pressure on the bolts? Or do you think it’s a matter of corrosion?
Good the bolts are intact.
Sharpen a pristine point on a small center punch or prick punch and drive the punch into the face of the allen head about half way in between the outside of the hex and the edge of the fastener.
Drive the punch at a 45 degree angle on the right side of the face (to reverse) to rotate the fastener out.
Just looking at the picture of the bolt I have to say I have only seen that style of bolt used to attach a “plate” that is no thicker than the depth of the countersunk flank. Is what you are calling a “block” actually a thin plate?