Fwd: double time signature + double style

[Éditions IN NOMINE]

Hi list !

I'm working on Strozzi's pieces for the organ, and I have to typeset a ternary passage beginning with à \time 6/4 in mensural style (C with a point inside) followed with a \time 3/2 in default style. I've tried this :

\override Staff.TimeSignature #'style = #'mensural \time 6/4
\override Staff.TimeSignature #'style = #'default \time 6/4
\set Staff.timeSignatureFraction = #'(3 . 2) %typesets a 3/2 instead of a 6/4
\override NoteHead #'duration-log = #1 %for white notation (thanks the LSR !)

 This doesn't work (no double time signature). I've also tried :

\override Staff.TimeSignature #'style = #'mensural
\time 6/4 s1. \bar ""
\override Staff.TimeSignature #'style = #'default
\time 6/4
\set Staff.timeSignatureFraction = #'(3 . 2)
\override NoteHead #'duration-log = #1

but it lead to a naughty space that's quite ugly.

I've wandered in composed metrics, but I can't figure out how to mix diffrent type of time signature...

Many thanks to those who are going to find THE trick !

JMarc