Dlduchon,

Heat works miracles on stuck bolts. If getting the engine hot doesn't work, try a torch on the bolt head. Try to get it red hot and apply torque quickly with the allen wrench.

If that and the other suggestions don't work, you might have to cut off the bolt head with the torch. Have a fire extinguisher or lots of water handy in case of a fire.

If you cut off the bolt head, arc weld another bolt to the remainder of the stuck bolt. The heat from the welding should get the bolt hot enough to come out.

One other possibility is to arc weld your allen wrench to the stuck bolt. The heat should allow the bolt to break free but you will have sacrificed your allen wrench but they aren that expensive

That's what I would try to get it loose.

P E H