I would never recommend an iron gear on a steel cam over time. However, I also don't know how to define what that time is, because it could be an expensive experiment and have no desire to try.
I REALLY don't like bronze gears, but knowing that the dual sync has a gear that will work, and this is temporary, and you can't find a steel gear, I'd go bronze. However, the cost difference between steel and bronze is minimal if you can find a steel gear choice.
You may want to consider a borrowed aftermarket distributor or even purchase a used one, much easier to find a steel gear
PM me though before you mess with that dual sync, I learned a lot about them (and Holley programming/operation) on my most recent Terminator X install and would be happy to share, especially if you are going Terminator X, although Sniper is very similar.