I have an Ancient Shenlong’s Fist Of Legend, and tried converting my Shenlong’s
Relentless Assault, but got a message that items have to have 3 pieces in the set to be able to be converted. The only reason I tried is because I read that someone did convert the Relentless Assault, but this was in 2018, so don’t know if it was able to be done and it was changed or the person told a big fat lie. All I know is I was very disappointed!
As far as I remember, the Cube recipe to convert set pieces has never worked on sets which only contain two items. That’s reflected in the official Game Guide…
https://us.diablo3.com/en-gb/game/guide/items/kanais-cube#recipes
During the ptr for the patch that gave us Kanai’s cube, you could swap ANY set piece for other pieces in that set, including 2 piece sets. You could also get ancients so it was SUPER easy to get good weapon and ring sets. It proved to be too powerful and they limited it to 3 piece set minimum and eliminated ancient (and primal) drops coming from the recipe.