Just don't do them both are the same time or the motorcycle's front end will dive, the machine will come off its center stand and may crash or cause you some serious hurt, or both.
If you are set on removing both cups (at the same time), be sure that the center stand is secured in the deployed position with a tie-down or a turnbuckle, you will need to weight down the rear wheel or use a tie-down between the top triple clamp and a rafter. I use a hydraulic lift/jack (made for larger cruisers), where I use tie-downs to secure the Norton to the lift/jack with enough wood to insure that the motorcycle is not bearing weight on the exhaust system, but rather the frame rails; not as straightforward as raising a Victory or a Hardley with flat bottoms
No matter how you support the motorcycle you will still need to load the fork sliders with about 25mm of sag, or you won't be able to get the fork cap nuts/damper rods up high enough to un-seat the jam nuts. If you strip the front end you can change the fork oil while you are at it; amongst other operations.
Before you begin, plan your moves so you don't end up needing three hands. Make sure that your tach/speedo are completely disconnected and that you have a safe place within reach where you can put the cup with the instrument installed; even if you remove the instruments prior to removing the cups, just know where you are going to put things (within reach), and you'll do fine.
