So would you characterize them as more Sabellian or Modalists?
I'm not sure. It's been a long time since I've read this stuff, but if I recall correctly the Modalists/Sabellians believed in a trinity of "modalities." The Oneness Pentecostals don't believe in a trinity at all. And I think some of them (Modalists/Sabellians) said J*sus wasn't real and didn't really die. The Oneness Pentecostals don't say that. They say he really died but that he was the one and only person in the godhead incarnated.
Come to think of it, you could probably call them modalists of a sort. Sabellians, I'm not so sure. But remember, heaven was vacant when J*sus was on earth (according to them).