Good Pics Chris, Having inspected, repaired & tested many thousands of Sterling SMGs in my Time as a Service Armourer. And also having visited the Sterling works when it was 'Alive'. I can state with hands on expirience that there is NO difference in the SMG series really. (That is to say the L2A3/ Mk IV ONLY) The 'Police Carbine' was simply a standard L2A3 (Mk 4) with a modified Trigger mech group for Semi-auto only. The Nomencleture on the Mag Housing was engraved differently also for the the 'Police' market. BUT, sales were aimed mainly at the Civvy shooter market. This weapon class was abused as it was VERY easy to obtain an Ex Military selective fire trigger mech & slip in the carbine. What you then had was a selective fire full auto, sub machine gun. A BIG No, No! So, Sterling revamped the 'Carbine' with a rework so it was closed bolt & striker fired version. Effectively making it semi-auto again & drasticaly altering the internal design, so that Ex Militray componant exchange could NOT be effected. Or modify them into selctive, full auto models. These were aimed at the US Civvy Market. The bottom photo is of a Replica, or Fake. ALL, Sterling Magazine Housings were ENGRAVED & NEVER Stamped with Numbers & Nomencleture. BUT, If Chris wants one just to hang in the rear bracket of your ferret only. No one will really see what is written on the Mag housing. So if it's cheap & welded solid. Does it REALLY matter? If it DOES matter, then there are LOADS of them available on the market, just short of three hundered quid! Good Hunting Chris!