That's what the pull cord is for.
I got just the differential here:
http://www.ereplacementparts.com/differential-asm-lrv-p-1755400.html
Yes, the outside gears are plastic, but the inside gears are metal, and on mine, those were the ones that were stripped out on the old one.
I got mine here:
http://www.ereplacementparts.com/differential-asm-lrv-p-1755400.html
I got my new differential here:
http://www.ereplacementparts.com/differential-asm-lrv-p-1755400.html
And yes I got the mower working again with it.
You can buy just the wheel and just a differential. I got the differential at:
http://www.ereplacementparts.com/differential-asm-lrv-p-1755400.html
Took me maybe 3 hours to replace it. I recommend replacing the wheel with the friction disk at the same time. It's way easier than fixing a car's transmission (and yes I have done that too).
Please post pics of the bent part.
Was the replacement made of any type of metal?