Upgrading from a very old version of mu, best practice?

Hey Gang, I have taken over a mu-workpress site that hasn’t been updated in years. It’s for a non-profit and has about 70 active sites on it.

It’s running 2.3.1 which I believe is really mu version 1.3.1

How should I go about upgrading, should I do it in steps, ie go to each major version first? or can I safely jump to 3.2.1?

I do know that several of the plugins currently used are not actively being developed, but we should be able to get around those, and find replacements. The only document I have been able to find is this.

http://codex.wordpress.org/Upgrading_WPMU

But it doesn’t address anything after version 3.0.X

Ideally I would like to take a backup of the site and do test upgrades, but my first attempt at modifying the db for the test URL hasn’t worked. But I’m still looking and reading.

Thanks
Damon