If you want a proper Ausf M you need the long barrel back (and probably a stick-on exhaust system?), you certainly have a paint scheme thats closer to an M than the N based on what I know...

I'll be back home in England to visit family in a couple of weeks, so if you decide you want the longer barrel I can pack one of my surplus barrels and post it up to you for free - just pm me to make arrangements.