[Tom Goldman]

I haven't done any in a while ,but I used to use old cast pistons ,busted them up and melted in a iron pot on a turkey fryer burner . skim off the dross before pouring.
Make sure you have enough to do the fill in one pour . It helps to preheat the head casting as well to prevent the pour from shocking the casting and keeps the aluminum from chilling before the fill is complete.
I used furnace cement and chimney packing to dam the crossover in the port side and filled from the manifold side .
Be safe , take your time.