filing the nozzle down would have been the simplest and quickest.
Any pound shop will sell you a file capable of doing the job, if you don't already have some.

And don't be so sure it's NOT a standard nozzle.
I've currently got three totally different sized 'standard' nozzles.
You have to read the descriptions really carefully before ordering, and even then there's no guarentee that a new 'mk8' nozzle will match the old 'mk8' nozzle.
Other 'mk's' are available and all just as likely to be random sized :-)

But other than that - just shave 1mm off the brass thread.