Ugh. I spent those same three days on my 54 getting that same pin out last week. I sprayed PB blaster and WD40 like there was no tomorrow.
Here's what I did: After I got the cotter pin out I put a finishing nail in the hole and tried to twist the pin after spraying it. To pound it I had to use a screw in a vice-grip between the hammer and the pin so that I would not flare out the end of the pin. It finally came out and I was sore! Once the pin moved enough to get the cotter pin hole into the fork I think that helped the WD40 or PB blaster to do more good.
Hang in there! Any more suggestions here?
Jen