The RCtank.de lower hull would work. Since the side flaps are plastic, you can simply cut them off and use styrene to obtain the correct Ausf. A profile, like you've shown in post #6. However, since you've already done so much work on the lower hull itself, I would suggest sawing off the lower glacis and replacing it with a styrene plate at the correct angle. From the pictures it looks like you have enough space in the transmission compartment to move the gearboxes a bit further towards the rear. As I recall, you only need to move the drive shafts about 10mm: