Fortunately edmehlig posted a Rumble copy of Lewis' casting video here:
Casting Tip: Mold Temperature for PURE Lead, (scroll down - it's towards the bottom of page 5) so it's still available. After watching the video last night, and reading your and eekjellander's responses to my question about multi-cavity molds, I think I'll stick to single cavity molds, despite the higher cost. I can see that it would be difficult to maintain mold temperature with a multi-cavity mold, and Lewis makes it clear that the right mold temp is critical to casting good bullets.