I’ve used my modeling clay (has oil in it so it doesn’t dry out) and I’ve added to the casting I made for my heel seat press. There’s no reason I can’t use that casting for both my initial last casting AND as the template for a press for the cork for my heel seat.
Once I get the initial mold made I can clean it up and do any final fussy shaping. The modeling clay fleshes out the toe and the top of the last at the ankle.