Steve has sent me an update on his progress.
The pattern is nearly there now, made up from ash (main body), MDF (flange), a bit of pine (core prints) and filler (the rest!).
Once sawn in half, the lost material was made up with some 30 thou plywood
and fillets were added using fillet leathers glued on.
The reason for using proper timber this time is that the moulder said that he didn't like MDF much as it tends to delaminate when trying to draw the mould from the sand. OK for a couple of uses but not much more. The plan is that he should ram up the flanged side first and then, after turning over, manually cut away some of the sand over the flange so thatwhen the other side is rammed, a piece of sand sticks downwards into the cavity but lifts off the pattern when the mould is split. No doubt time will tell as to whether it works.
He is now pressing on with the core box and this should be completed tomorrow.
Next part will be the main pump body.
Our thanks to everyone for all of their helpful comments.