Most old vintage turntables made in the United States used regular automotive motor oil. The Rek-O-Kut, for example, used SAE 20. That said, Photon46's suggestion of a heavier, but similar, oil is a good one because the heavier weight provides a bit more dynamic braking. That's a good thing, and the Papst motor on the Empire can easily handle the extra drag on the system.
If you want to be a little more adventurous, you could try some of the more modern oils. Recently, I lubed a Fairchild 750 transcription turntable with a heavy weight of synthetic Royal Purple industrial grade oil. It was SAE 64, if I remember correctly. I also put a small amount of Royal Purple grease at the bottom of the bearing well. The results were very nice.
If you want to be a little more adventurous, you could try some of the more modern oils. Recently, I lubed a Fairchild 750 transcription turntable with a heavy weight of synthetic Royal Purple industrial grade oil. It was SAE 64, if I remember correctly. I also put a small amount of Royal Purple grease at the bottom of the bearing well. The results were very nice.