Dragonhelm
Knight of Solamnia
Instead of swapping the time period, how about an alternate timeline? You take most of the core of the setting, but then change a few key bits that take the history in a different direction. So it is still in the same timeframe. Old setting material is often 75% compatible (in the story, not mechanics). The geography, climate, customs, etc. are much the same. But the story line, threats, etc. are very different.
We already have six alternate timelines from Legends of the Twins. Perhaps one of them might fit.