Congrats on overcoming the biggest challenge with hardware, seizure!!!
Here are a couple of suggestions from my belt of experience with that particular bolt. Use a brass drift (1/2" or larger), place it on the head of the bolt and give it two good blows with a 2.5lb hammer. I use a wrench to see if I can feel the immediate give from the static tension on the bolt. Tighten the bolt just until you feel it give, than try loosening it. You will know if it is going to break free or not.
If the bolt does not break free spray it with Wurth Rost Off than drive the car for a couple of days, than give it another try. If it feels like it is not ready to turn clear the timing cover area from any material that could ignite or catch fire. Use either a propane torch or the handy butane crack pipe torch and while KEEPING AN EYE ON THE FLAME heat the threaded boss area of the timing cover. After 3 to 5 minutes of heating spray it again with Rost Off, tighten first than loosen.
This technique has worked well for me, maybe it will work well for others.