gas, flame and oxygen of course. IIRC Mike had a scare with it, and didn’t want 100s of people copying it especially if it went viral with ID10Ts like MrTeslonian.
The timeline is all mixed up for me. And there were patent trolls on the yahoo list. So any open discussion like ‘hey why don’t you try xxxx’ resulted in xxxx getting patented. Mike really didn’t like that.
This patent expired because of non-payment though:
BTW I was trying to say OMG that isn’t original or dissuade you from doing it. 
The only criticism I would have is the bell coming down is going to be a heat magnet, and probably melt quickly.
One of the key aspects of the nozzles, and I don’t know if many do it or not, is you are trying to get even oxygen over the whole bed and reduce channeling in the bed, and other flow issues.
The only gasifier I can think of offhand with nozzle pointed down is the Kalle which is a charcoal gasifier and supposedly fairly popular. But that reused exhaust gas to limit oxygen.