I have your sump plug tapped to 1/8 NPT-27 sat here on me desk, will post in morning for you.
The reason why the hole isn't dead centre is because the "nut" part of the plug isn't in line perfectly with thread part, bloody shocking quality really, they are obviously just spat out of a machine, it will do the job perfectly though, they are a very hard metal(lot of carbon) not quite 10 form hard but plenty strong enough.
tabetha