Vibration, good quality penetrating oil, and time are your friends. Time means hours, maybe weeks, I have spent months. There was a long ago story on brit-iron of an engine retrieved from the bottom of a lake after many years. The owner went through this process for 2-3 years but it came apart. I just spent off and on for a week tapping and gently pulling on some bathroom fixtures in place since 1960. Came apart eazy peazy. But p-a-t-i-e-n-c-e.
Love all, rick
1963 BSA Rocket Goldstar, 1969 Triumph Tiger, 1969 Norton Commando, 2017 Yamaha FZ07, 1955 Ford Thunderbird