Titling and grouping

[Jose-Luc Hopital]

Excuse my poor english ...

2 questions:

1) I'm currently keyin Corelli's sonatas in wich each movement
have a tempo indication (Grave,Allegro ...) . For that , "piece"
in the header block work fine. But there is also a dance indication
( Gavotta, Corrente... ) wich must be centered above the first
system . Subtitle in header block work only for the first movement
and I need this centered title for the 4 movements.

2) I have now a set of directory on the same level : one for each
sonata with ~ 30 files in each ( op1_1/*.ly ,op1_2/*.ly ...). What is the 
easiest way to obtain score and parts of the entire opus: i.e.
the score or parts of the 6 sonatas in one document.

Thanks for your help.