I regard my first responsibility is to inspire people to build and complete a kit and enjoy as much of the social aspects of modelling as possible. Another responsibility is to ensure that we all make as much of an attempt as possible to follow the rules.
Of course, when dealing with history, I accept that I and most likely everyone else alive today, don't have 100% understanding/knowledge of events back then.
So, in a case like this, I have some latitude. But, I feel it is another duty to look around and see what information I can find on the subject.
Here is a quote I've found on a forum regarding Panzer Tracts 3-3:
The Bases for the Asufuehrung identification within the 8.Serie/Z.W. are the main armament and provisions for increased fording ability, as follows:
Pz.Kpfw.III Ausf.J armed with a 5 cm Kw.K. L/42
Pz.Kpfw.III Ausf.L armed with a 5 cm Kw.K. L/60
Pz.Kpfw.III Ausf.M armed with a 5 cm Kw.K. L/60 and outfitted for increased fording ability
Pz.Kpfw.III Ausf.N armed with a 7.5 cm Kw.K. L/24 and outfitted for increased fording ability
While the Pz.Kpfw.III Ausf.J with the 5 cm Kw.K. L/60 where produced from December 1941 to March 1942, they where all officially renamed Ausf.L in April 1942.
So, as the authors are well regarded, and history about such minutiae is always a bit foggy, I'm going to allow it. All of the dates within the quote fall within our historical campaign dates.
Here is a link to the thread: Pz III J/L
Good luck and happy building!