Overwrite key signature with numbers

[Robert Mengual]

Hi, I am trying to overwrite the key signature for my custom music notation so that instead of displaying the sharp and flat icons, it shows a given number and the alteration. So, for example, E Major would show 4# instead of ####.

I have been able to get the desired output by hardcodeing it using the markup function. However, I am not finding a way to conditionally render the number and alteration depending on the key. Could somebody help me? 

Here is my tiny hardcoded example, with a screenshot:

\version "2.23.6"

\layout {

\context {

\Staff

\override KeySignature.stencil = #ly:text-interface::print

\override KeySignature.text = \markup {

\combine

\halign #-1 \lower #1 \musicglyph "four"

\halign #-5 \musicglyph "accidentals.sharp"

}

}

}

\relative {

\clef bass

\key e \major

cis dis e

}