Hi Alan, I built the model in SketchUp, of which the basic version is free. I however, would probably recommend Fusion 360 because of its parametric capability, even though it's a bit harder to learn. (it does better with curvier shapes)
I cut one of my failed castings in half to check on the metal quality & ports. I cleaned it up a smidge, but this is before boring, machining or porting:
