Replacing drive gear on a Singer 498?

I believe I have the same problem as Ian "Singer 498 Feed drive shaft gear?"
I have the long worm gear broken on the longer of the two shafts in the top of the Singer 498. I believe I have it identified on the www.homesewing.co.uk/parts-database/gears/singer-feed-worm-gear.htm website as 422408930. Can anyone confirm this is correct ? Also should I replace the other gear (I think 383273000 but picture on website does not look like my gear) and where can I get the correct fluted allen key, what size is it (I have a set but this size is not in it), and the info on retiming ? All assistance gratefully received.