When putting the burners back make sure the center of the back of the burner goes over the orifice nipple. and the front little pimple goes into the little dimple on the tray.
If it is in correctly it will not move side ways. then put the screw back. now the tray and burners should feel like one piece the burners should no have any play in them at all. Make sure the pilot tube and the thermocouple are facing towards you. Now slide the tray back in.
Line the union up and make sure both tabs drop back in there slots on the left and right side of the tray. Now normally I would just say tighten up the union but we have to replace the gas valve first.