I think the best way to do this is get the rail unstuck so you can get the pump out. Have you tried using a spray penetrating oil like PB Blaster, Kroil…? I am assuming it is rusted in place but if it is stuck for some other reason please explain why it is stuck.
And do you really know how to remove it or are you just using the common sense method? I can’t tell you how since I don’t know but perhaps
@North Idaho Wolfman,
@whitetiger or
@Hugo Habicht will be along to help.