Picked one of these up for that sort of thing at the local welding supply house.It is possible, but since it is a straight shot into the cylinder, you should be able to use a pipe cleaner or small carb brush to run through and clear anything (or confirm that there isn't anything blocking).
Indeed it would be difficult and would depend on your welding skills if it was something you would want to attempt, I would do it with my mig welder or Tig if thats something you have but it's not something I would attempt if stick was your only option. I don't think it being hardened is going to matter in this case.Man? That would be very difficult to weld
Isn't the crank hardened?