I also saw mention somewhere that this is V2 of Starship upper stage? Somewhat longer, and I’m sure a bunch of other changes to enable mass simulator deployment.

Yes, about 2m longer. Also some modifications to the heat shield, including testing new types of heat shield tiles. Also non-structural versions of new catch pins to see how they perform on reentry

Edit: also, they are reflying one of the raptor engines that was on the previous flight (Engine 314, because pi).