[Marshall V. Daut]

If one is going to replace the field coils anyway - and not simply remove them to clean the inside of the housing and/or re-seal the coil wrappings - the best way I have found to remove those stubborn bolts is to use a torque and heat the bolt heads until cherry red. Allow them to cool and you can then very easily back the bolts out with a large screwdriver. 'Still won't come loose? Apply heat again. They WILL come out when persuaded by heat.
I have tried all the recommended rigs and special flat blade socket with impact wrench, but heating the bolt heads is by far the easiest and quickest method, let alone less stressful. The bolts can be reused if the heads and slots have not been chuggered up by past attempts to remove them or to stake them in place. To be safe, just order two new bolts when you send for the new field coils. Why get cheap at this stage for the sake of two measly bolts?
Marshall