working directory umask

Hi all,

So for one project at work, we have a (slow) server with a common 
build area.  Standard practice has been to extract a tarball, 
configure, make, make install into a common area.  I have started 
using git to replace the tarballs -- keep version info, make doesn't 
have to rebuild everything, auto-tag install sources, etc.

One problem:  Even though the working directory is g+swx and git was 
initialized with --shared=group or --shared=0660, the checked out 
source files still don't have group write permissions...

Is there an option that I've overlooked?  I can't seem to find 
anything that overrides umask in the working directory, only in the repo.

Thanks,
Daniel