well with out seeing it and knowing how bad we are talking and where exactly it is rusted....I would say take the nose plate off and anything that will come off, deal with those separately. the main sticking point is likely the main shaft ( runs from the hand wheel clear to the needle bar. might try some kerosene, hydraulic oil or something like PB blaster.
soak it down let it sit. tap on the end of the shaft with a rubber mallet ( just a little vibration not trying to bend or force anything) get a old of the main shaft where the handwheel came off and try to wiggle it. even just a smidgen and you are winning. turn it upside down and soak down inside the pillar good and all the metal to metal contact points underneath. I can not imagine that with patience and penetrating oil that you can not win. clean up the exposed parts of the needle bar as best you can... when it starts to move you don't want to drag any additional crud in there .
Slow gentle and clean each time you try... oil and wiggle let set wipe off rust and dirt that may have flushed away... wiggle and flood more oil repeat as needed.