It would make sense that the increase should mean that you have the same engine block for everyone, EJ207 and EJ257.
Then, for 207, you press different sleeves.
This is a factory efficiency improvement and I suspect an engineer somewhere would get a raise for unifying the process for the two engines, because of saving costs.
Maybe, if you want to carefully wipe the topside of the sleeve, and take a photo, we could see this.
Other than this, my theory is based on your observation and idea, that this is basically the same block as a 257.
They basically CAN make the 257 into a reliable engine at the factory, because... they can do anything, they are the factory..
.
We already know, from the built section that the sleeved engines are the ones that can support increased power and torque so "sleeving" a EJ257 to make it a 207 is not a bad idea.
Then of course, they give it the 207 rotating assembly, which stops the piston at TDC below the deck, another feature that makes it more reliable.
Yes, it makes sense.
Ok, now as far as pistons.