Way too hot for any epoxy.
Epoxy might be OK in the intake port near the intake manifold but anywhere near the seat it will fall off or burn. a little roughness is inevitable and won't affect flow any, I wouldn't worry about it unless the seats are barely hanging in there. If thats the case they need to be welded not brazed...regular brazing won't last either. Aluminum bronze brazing is suitable however, many aircraft valve seats are constructed of aluminum bronze.
Epoxy might be OK in the intake port near the intake manifold but anywhere near the seat it will fall off or burn. a little roughness is inevitable and won't affect flow any, I wouldn't worry about it unless the seats are barely hanging in there. If thats the case they need to be welded not brazed...regular brazing won't last either. Aluminum bronze brazing is suitable however, many aircraft valve seats are constructed of aluminum bronze.