I just had the same issue with a Suntour New Winner freewheel and Campy NR hub, and took it to my LBS which knows vintage gear. I already had the factory Suntour CroMoly freewheel tool locked in with the skewer. They have a very nice old and heavy vise bolted to their wall anchored work table. They used some penetrant oil and let it sit before using leverage to get it loose. I was quite thankful and will remember to grease the threads or use anti-seize on the next one.

Same thing for a Campy pedal on my Campy triple, I let them handle it so I wouldn't have to struggle with it since I don't have a good vise setup. In many cases, the relatively minor cost really outweighs the time, hassle, and worry if one doesn't have just the right tools - which in many cases I do but when time is short (Eroica prep), better to let the pro do it for now, IMO.

That said, I just bought some additional PB Blaster and other products to help stuck fasteners and parts. Back to the workshop tonight!