Scott Bowden in his book Napoleon and Austerlitz (p.384) has a detailed map of the northern portion of the battlefield. It seems to show the starting positions of both sides. He has the guard just to the east of Bellowitz, and Oudinot's grenadiers just south of the guard. The 1st corp is in front of both, with its right flank in Lapanz.
re Songis. Although Bowden doesn't actually say if Songis was in direct command, the Grand Parc d'Artillerie was (according to Bowden) positioned on the Santon, just to the rear of Lannes' corp. It is listed as 18 pieces - all captured Austrian 3prds.