I can see where the confusion lies, you led us to thinking you ere referring to a crank bearing because you called it a 'main bearing' it's the gearbox output shaft bearing isn't it.
I've just been on the phone, if you send your old bearing to bridge engineering in Stalybridge they will see if it's the same a 6304NR they arent sure what the prefix NX is
Glad to have been able to help bippo yeah it wasn't too difficult I bet even drewpy could have done it but that nut would have stumped him for hours haha
The fog never lifted all day and it's as bad as ever now !
if you press each ring into the groove in the piston will they bottom out they should do, if one wont then swap them over and try again because one of them may be a keystone ring