My red-bellied displays pretty stereotypical general parrot body language, honestly... nothing really stands out as being all that uniquely poi.
She's an expressive and easy read for sure.
Nonetheless, here's what I have visuals for:
When she's excited (usually on seeing a favorite toy), she does a really exaggerated head bob - not like regurgitation, but... nodding, I guess.
Relaxed means it's time for Orb Mode.
If agitated, she'll fluff her hackles, hold her folded wings out, and click her beak rapidly while swaying her head side to side like a snake. Always gives ample and clear warning to back off.
When curious about something, she'll stretch herself very long or tall, often rising up on her toes.
Wants scritches? Head down and neck feathers fluffed.