We are using the Sammy case behind a 1.6 16v, with 4.24 gears in the Sidekick Case and haven't had any issues. (lots more torque passed through it then stock.)
I'd suggest if you want to put any real power through the Sammy case that you either buy or build a 'bucket' or cradle to reinforce the external case.
You can see our home-made 'bucket' here.
