Did not think it would be so simple, wrong muzzle brake for the earlier version though. Time to ponder.
Pzkpfw IV Ausf J had three return rollers not four, no turret side vision or pistol ports. Ausf F1 short 75mm Ausf F2 Long 75mm with ball muzzle brake Ausf H No side vision or pistol ports for the driver and signaller No extra radio antennae for the Panzerbeobachtungswagen version So unless it is an Ausf F2 with a later muzzle brake (or I am imagining that it is not a ball type) I am stumped.
Getting your own back eh, I even looked at the Panzer III Ausf B and going exotic with the Panzer IV Ausf G with Hydrostatic drive. All wrong hull shapes though.
You trying to confuse me, that appears to be one of the Pzkpfw III fitted with the Pak 38 50mm weapon, demonstrated to Hitler on the 4th April 1942. As far as I was aware that never went into production (Muzzle brake was never fitted to the Kwk 'tank' version). Always happy to learn some new things though.
Looked at the main weapon and what pictures I have for a Panzer IV View attachment 14823 Here is a picture of a trials Panzer IV with a Kwk 39 L/60 50mm. Like the Panzer III equipped with this weapon it has no muzzle brake as opposed to the Pak 39 version which does. Looked to see for other versions of the KwK 39 L/60 50mm and found this from a Puma but even though it has a muzzle brake it still does not look right. View attachment 14824