[Doublepumper]

I'm thinking epoxy won't take the heat in that area and will eventually fail. Silver solder doesn't work well for a filler. Brazing with bronze rod may be the best method to fill it without imparting too much heat and distortion. That's a tough spot, due to the uneven thickness and hole edge. Good preheat and slow cool will be the most important things for success.
Good luck!