NAF – New artifacts with unique properties.

I wouldn't say there will be too much imbalance. Both of these artifacts are quite difficult to find. As it turns out, resistance cannot be added, so it will simply increase the main stats by +6, like Sar-Issa (+1 from boots, +2 from armor, +3 from the combination), and add morale and luck.
It could even be made into an ancient relic so that it cannot be removed.
The Armageddon's Blade, for example, gives much more.