I had a much more fundamental question - where exactly to find the Mold function in Cura 2.7... it is not obvious! Answer (I found it): it is a Special Mode that must be made visible in Settings...Configuration settings visibility.
I plan to create a dissolvable mold in PVA, for molding silicon or any elastomer (then to think about splitting it for creating reusable molds in PVA).
I need to figure out how to somehow trim the safety margins in Cura (Ultimaker 3 firmware is not agreeing on the margin calculations, and even the non-mold print barely fits rotated at 45 degrees - I might have to rotate it at 45 degrees also in the Z dimension - ugly and wasteful of PVA...
Any comments or suggestions will be much appreciated!