I go with Dave. Try the PB Blaster first. I don't know how well it will work on SS+bronze but I've had good results with it in a lot of applications. It is my Weapon of First Choice.

If you need to resort to heat you can try a trick I've used a number of times with SS machine screws in aluminum. If you have access to an arc welder clamp the ground to the winch base and a plain steel 1/4" rod in the electode holder. Set the welder for about 100 amps and short down the rod onto the SS shaft. You don't want to make an arc but the current will create heat at the SS/bronze interface. Watch the SS pin closely and when it starts to turn a bit yellowish you can take the heat off. To avoid making pits in the shaft you could make the contact first then swith on the welder. It might take a couple of cycles. For small screws (1/4" and less) I've done this with the cranking battery and jumper cables.