I realize there's a Stack Overflow question: http://stackoverflow.com/questions/277029/combining-multiple-git-repositories

But I haven't found git-stitch-repo to be quite the tool I'm looking for.

I also consider this more of a sysadmin task.

How do I take code from an external repository and combine it with code from a primary repository while maintaining history/diffs and branches.

Use case: An outside development team using SVN has ported to git and now wants to 'merge' their code in to the main company's git repo.

I've tried subtree merges, but I lose the history.

I've tried git-stitch-repo, but that process results in an entirely new repo that's missing branches.

I just want to slot in some outside code as a sub-directory in our current main repo with as little disruption as possible and while maintaining the other project's history.

Any success stories out there?