The bore distance is the same. I think the main bearings are the same. So, the cranshafts should fit in all blocks. I think the cylinder heads are also interchangeable, i.e. boltable to all the blocks (i.e. 1.25 head can be bolted to 1.6, per example). Sadly, I think the oil and colling ducts on 1.7 block and head are different to the rest of the sigma (ZETEC SE) family.
Hope it helps