Its in post 140 here is another picture in this link that may show the motor better in this link under
Mercury 635 the far right you can click on it to enlarge it i cannot copy and paste picture here as its clearly copyrighted.
I see yours is missing the round stone wheel which has a rod going thru it with a small brass gear on its end in that assembly is the lever the contains the flint.
I can take a picture of mine if you need to see it.
You may need a donor engine for one though as i do not think these are reproduced or with some luck
Robert Grossman Marx parts man may have one as he does carry some parts not listed just mention it for an electric #635 as the windup sparkler is different although i did not see one on the not listed list he sent me when i ordered some CV parts.
Your motor will polish out very nice as the grease and oil actually saved it from rusting out the surface rust will polish right off, your shell i wish i could say the same as that rust on it will only worsen with time in my opinion .
I lucked out as my shell was rust free.