Chapter-subtitle and a short version of a( long) chapter title to fit in the header

[Robert Blackstone <blackstone.robert@gmail.com>]

Dear all, 

Presently I’m restyling a PhD-dissertation to make it conform to the requirements of an external publisher.

One of the items is the form of the chapter-heads.
What would be needed on the first page of a chapter, Chapter 1 for instance, is:
 
- Chapter 1  (midaligned, boldface, smallish size (\tfa))
- some vertical space
- Chapter title (midaligned, SmallCaps, slanted, \tfc)
- some vertical space
- (for some chapters) Chapter subtitle, (midaligned, SmallCaps, slanted, \tfb or smaller)

Furthermore I would need a header with the chapter-title on the even-numbered pages and the section-title on the odd-numbered pages.
The problem here is that some of the chapter titles are too long for this and they overlap the pagenumbers in the header. 
That is why I would need a shorter form of the chapter title and in some cases a main title and a subtitle.

As far as I know, in the command to start a chapter there is no possibility to introduce, in addition to the special version of the title for the ToC, another special, shorter, version of the title for the header.   nor a subtitle. 

I use:

\startchapter[bookmark=,list={Accompaniment in the 16th and 17th century and the development of BC},marking=,reference=ch:HistDevel,title={Accompaniment in the sixteenth and seventeenth century and the development of basso continuo}]%[a=a,b=b]

For the headertexts I use what I found on  http://wiki.contextgarden.net/Headers_and_Footers and it works quite well:

 %%%%%%%%%%%
\setupheadertexts[]
\setupheadertexts[\setups{text a}][][][\setups{text b}]

\startsetups[text a]
  \rlap{\sc \getmarking[section]}
  \hfill
  \llap{\pagenumber}
\stopsetups

\startsetups[text b]
  \rlap{\pagenumber}
  \hfill
  \llap{\sc \getmarking[chapter]}
\stopsetups
%%%%%%%%%%%

So my main problem is that I need, in the command \startchapter, a third form for the chapter title to fit in the header and a compatible version of the setup for the headertexts.

I did try to extract that from the ConTeXt wiki but I soon got lost.

Thanks  in advance for any help.

Best regards,

Robert Blackstone

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