Yes, you can take the cap off. At the front of the cap, under the chrome nose, there is a flat metal blade. If you push the blade back, or strike it with a screwdriver and hammer, the cap will open.
On some caps, the blade is recessed and hidden, but if you can fab a tool to get under the front of the cap and push on the blade, it will open.
It's a little hard to explain the blade. Send me your email in a PM and I'll email you a picture if you need it.
Once the cap is open, it is pretty easy to remove the tumblers so that any key or screwdriver will open the lock.
The dual petcocks are one for each carb, but a single petcock is all you need, and will provide plenty of gas to both carbs, and will simplify things.