About Cooey 84 firing pins...there were 2 types.
The early guns (from 1948 until?) had a different firing pin than the later ones.
My gunsmith laid all of this out for me.
The early ones were inserted and then Cooey installed a little spring clip with some special tool. If there was a way to remove this clip properly he's never found it.
When you have to change out the pin on an early one, the only real way is to drive out the pin and this dislodges the spring clip.
Then, to reinstall a pin, you have a headache as there's no way to retain it. So, you have to carefully measure, drill a hole, tap it, and install a retention screw as found on the later models. You have to use one of the newer pins.
The newer pin has a flat and the screw goes in and just short of that flat. If it went any further in it would lock the pin. The screw prevents the pin from falling out, it hits a little shoulder.
The later guns (from what year?) have a phillips head retention screw holding in the later firing pin.
The early pins are Unobtanium.
When you have a firing pin problem with the early guns, it's a PITA.
Later guns, very easy to deal with.