Hi @firemunki! I have a spare 105 rear derailleur in my hands right now with stock shimano jockey wheel in it. The tension pulley has a millimeter or less of play in it. The centeron pulley lot more play…more than 2mm but less than 3mm I’d say.
Both pulleys are about 8mm wide at the metal flange.
I don’t know if this helps but there is some info for ya!