Hi Bill,
You really did a good job on the "Dicker Max" there.
The only thing that is off a bit is the story about the K.Pz.Sfl. IVa.
It was originally developed in 1939 by Krupp in the Grusonwerke in Magdeburg. The demands from the Wehrmacht where to design a vehicle with enough firepower to be able to destroy bunkers and penetrate armour (under a 30 degree angle) at long ranges (over 2 km's).
Krupp started to design two different vehicles, both based on the PzKpfW-IVA. The first would be equipped with the 10.5 cm schwere Feldhaubitze K 18 L/52 (which was conveniently produced by their neighbours) and the other with a 12.8 cm gun.
Because the 10.5 cm gun was produced next door and it was easier to install, Krupp settled for the K-18.
Eventually 2 vehicles where produced as prototypes (even though Hitler wanted to start serial production right away) and where sent to the 521st Panzerjäger Detachment for a proposed attack on Gibraltar. When this never eventuated, they were transferred to the 3rd Panzer Division and saw combat on the Eastern Front in 1941.
Eventually one prototype was captured by the Russians after it got hit. The hit caused a fire, resulting in the ammo to ignite rendering the vehicle useless.
The second vehicle was then sent back to the Grusonwerke in Magdeburg to be refitted as a normal PzKpfW-IV.
The serial production of the "Dicker-Max" never started because the Germans decided to build the Nashorn instead. That vehicle could be produced a lot faster, but also packed less of a punch. Looking in hindsight, serial-production of the "Dicker-Max" could have proven to be more useful since it's 10.5 cm gun would even have been lethal for the later JS-2 tanks.
Greetz Recce