I agree that heating the casting will be risky but I do think it is the best way to remove the fitting without destroying the female threads. I wonder if it has thread locker on it to stop a prior leak, in that case the heat will do the trick. Slow and gentle will get you there.

1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy