Regarding the battery tray location, if you look in the wheel well you should see one or two nut/bolt holes, there is also a bolt holding the tray near the front (rad area, I thing the neg ground cable is also attached at that point as well) if you undue these the tray lifts right out. I learned this the hard way because my wheel wells had years of undercoating in them and I tried to remove the tray from the top and I thought the tray was welded in.

__________________
Marc-André

W115 1975 300D "Geraldine"
W115 1976 300D parts/tutorial car