that Headset cap can be stubborn to remove..(the black cone on the the steering).. there is an o-ring seal inside of it, and they get stuck after several years in the rain...
there is also a wedge that holds everything together too.

i put a 2x4 piece of wood on top of the fork's Steer Tube, then use a 3 lb.hammer on the wood.. they move, eventually..
i just removed one last night.
pre-cleaning the rest of the steerer tube will help, once it breaks loose some... scotch brite scouring pads do a fantastic job, without removing the remaining metal.
Don't use scotch brite on aluminum, unless you intend on Completely refinishing that part!

WD-40 is a Lousy penetrating oil... it is mostly a Solvent, for cleaning.
i use PB blaster... Kroil and CRC Penetrant work great too.

put some penetrant on that master link, then use a pair of needle nose pliers on it, squeezing the rollers at either end together... it SHOULD click inward to where the pins are in the larger parts of the slots... you can then work the halves out of the rest of the chain.
option 2... use your chain tool to push ANY pin out of the chain, since you should probably replace it anyway...

are there any parts of the chain that are frozen stiff with rust?
does the chain feel rattly or overly loose/noodley when you move it?