Robert, can you define what you mean by a straight factory L?
Might be making things difficult for yourself by trying to draw a line of when the J gave way to the L. They shared details of changes as they were both being produced at the same time for about a five month period.
You had also stated earlier that IIIL production did not begin until June 1942, but Jentz research has it has Dec. 1941:
You are correct about the overlap in production. In fact the J/L's were L's that made from the start of a J.
Panzer III Ausf.L TP production vehicle, beginning in early 1942, was a transition model equipped with the Ausf.J turret and the standard long barrel 5 cm KwK 38 L60.
Sometime around March or April a prototype was fitted with the KwK 39 with a modified muzzle and muzzle break, but it was never produced. At that same time they try to fit a PZ IV turret on to the III. That didn't work either.
In late May the turret with 57mm of armor was mated with the 5cm KwK39 L/60, sans muzzle break. The new production run also began installing a torsion-bar counter-balance instead of a coil spring for the main gun, and altering the air-instake louvres and hatches on the rear deck.
As well the hull escape hatches on the hull side, the loader’s vision port on the gun mantlet and the turret side ports were deleted. A system designed to transfer heated engine coolant from one vehicle to another was also introduced.
All these changes created the Ausf.L production model.
The order placed in May for 1100 units was reduced in June to either 1000 or 900, depending on the source. I'm inclided to think it was the former. Of these the first 600 were sent to the Eastern Front.
450 of them were mounted with the 7.5cm KwK L/24. Also 447 Ausf L were used to mount the short 7.5cm gun and thus became Ausf N. One was completed even with an experimental, tapered-bore KwK0725.
The projection L's saw service with the 1st SS-Division Leibstandarte Adolf Hitler, 2nd SS-Division Das Reich and 3rd SS-Division Totenkopf, and the Panzergrenadier Division Grossdeutschland.