If you have SW14 or later, you can use the Intersect tool.
You can intersect solids, surfaces, or planes to modify existing geometry, or to create new geometry with the Intersect tool.
For example, you can add open surface geometry to a solid, remove material from a model, or you can create geometry from an enclosed cavity. You can also merge solids that you define with the Intersect tool, or cap some surfaces to define closed volumes.
Thank you for your concise answer.
My late acknowledgement was due to an all absorbing non-CAD process development project that arrived early in January soon after the one which promted my question had been completed, and an email just received from SW Comnunity Manager, reminded me of my posting.
Yes, I have SW 2014, and will give SW Intersect Tool a workout on the received mould model that originally promted the question.
Thanks again for helpful guidance.