I just watched a youtube video of that game. I have played similar games decades ago.
How do you create your dungeon? If you use cube blocks then you need to arrange them. And in the end you will arrange them as a grid anyway. So you will have grid movement. Which is your distance movement.
What is so wrong with the first sample i gave you? It works for FirstPerson View as well. (How should I implement grid based movement - Character & Animation - Unreal Engine Forums)
The first screenshot shows you how to check if there is a wall:
You press forward once, the look direction of the character tells you which direction you want to move the character within your map. And then you just need to implement the screenshot. If the hit result is false (no wall or closed door) then you can execute the second screenshot.
The second screenshot shows you how to move the Character. GridSize 100 where 100/2 is the middle position of the cube.
And the Timeline handles correct movement over time to the target distance.
Just try this on a simple plane, you will have your “distance” movement like that in any direction you look with your character. And you will get the Grid-Movement for your cube blocks by snapping rotation to 90 degrees (like you see in the Grimrock game).
Hope that helps 