A bloke down in Melbourne used to make these for us from billet.
He didn't have the data to cut anymore so we have recently sent down one of our gear sets for him to copy.
I've never managed to break one of these gears and believe me it wasn't for the want of trying.
They don't require any mods to install.
Hopefully I will be able to supply these HD gear sets shortly.
Cheers,
Brian