Leave the jumpers as they come. You need to do all your tweaking in the bios. If you want 83MHz fsb, then go change it in the bios to that. While you're there, you may as well bump up the voltage too, because you'll probably need 1.7 or more. Also, do not have anything on your hard drive, especially at 83MHz that you cant afford to lose, because there is high risk with an out of spec pci bus speed like that. Have you already tried for 100MHz? What kind of cooling do you have? A C2 600 is a tough chip to overclock.
Edit Be sure to disable speed error hold in the bios. That will keep you from getting the "CPU Unworkable or has changed" error.