Well after taking out all the plugs and I soaked all 16 of them in a pail of diesel overnight.
So far three out of four I tackled came apart with tapping around the ring and cover and a propane torch and the strap wrench did its job. I need to pick up a 1-9/16 socket tomorrow to use my impact on the other.
This one the Centre has pins holding it in. The others don't have pins. Are they soldered in??