My own Figured Bass number set, where do I start?

[Nils]

Hello,

my pusblisher wants baroque figured bass gylphs. They have the strokes in 
different places than the Lilypond versions.
I guess nobobdy did this so far, so I have to do it myself. 

Where is the point in the code where I have to start? I want to do it right and 
use the same lilypond syntax like 4\+ or 6\\.

Whatever I do will be made public again, I am willing to do the work. But a 
little starting help would be nice.

I know Scheme, btw.

Nils