Because of the high pressures, a grease is preferred - I use Sta-Plex ultra high pressure grease. It has the highest "Timken-OK" rating that I could conveniently find and has very high "stickiness". Bought a tube about 10 years ago and still have 90% of it.

Re headstock spindle oil - why not just use headstock spindle oil? I bought a gallon of it years ago from MSC for my South Bend and it does what it's supposed to. The bearings don't run hot.