3rd level with space XKB

I have gone through plenty of documents and spent a lot of time trying to configure it, but so far unsuccessfully. I have keyboard with the 3rd level keys (probably ISO_LEVEL3_shift ?) So when I press Capslock and at the same time A, I get a acute.

Is it possible map it instead of Capslock the space? I imagine it as when it is pressed with the key, then it is switcher otherwise it is just space. I am not against experimenting but show me, please, at least direction (if it is possible)