What to replace-A833 rebuild
The dog teeth come with the sychro assembly (at least that is the way it used to be from mopar) the new suppliers (passion) may have them separately.
For the third gear, if you can get a clear and close picture of the small teeth, that would indicate the condition. You have to look very closely. These teeth (and the slider) hold the trans in gear. A trans popping out of gear drives me nuts! (been there). Its all what you can live with.
The brass synchro rings do nothing to hold the trans in gear, that is the function of the slider and the gear itself. The sychro ring function is to act as a brake on the gear as you are shifting. The slider ring pushes the sychro ring onto the taper and brakes the gear (so no grinding). The bevel on the small teeth (on the gear) lines the teeth up to get engagement. The dog teeth keep slider centered (sort of a detent). If the teeth are worn the slider will float around. The dog teeth also locate the sychro ring and keep it coupled to the slider hub.