We've remastered the SIG33 model in CAD, and it's on the way to being cast. Look for it to appear in the web store very soon.
Part load out of the new kit. The superstructure (light blue) will be modular, allowing the hull to be used for a number of other kits, including the SU76i and Panzer IIIJ.
SU76i Part load out 
Panzer IIIJ
Production Cat model in resin and metal released this week.
We are using the same approach to make the Stug IIIJ as well as the Stug IIIG. Both tanks are made by adding on a new turret/suerstructure.
Currently, this model will include the SU76i, and eventually replace our Panzer III and a full kit of the Bergepanzer. I imagine it can be used as the basis of any variant if there was enough interest.
Brent, I like the idea of using this for the SU76i since no one has done that yet. As for the Panzer III J there are two other companies that currently have them out. May I ask what else you are thinking of using this for? Joe