you bought a kit for hyperglide freehub, bub.

bummer.

if you grind off the gear teeth, you will play hell ever removing it without cutting it off.

you should have chosen a hyperglide freehub.... a DA 7400 hub would work fine.

if you're using a tensioner for the chain, you could use that hub and cog... and have an optional high gear available...

1.37 x 24 tpi... now where have i seen that thread size... hmmmmmm... hint: it's a common bicycle assembly.. (the old styles used a Hook Spanner to remove the LOCKRINGS....;-)