The Sherman's 75mm gun is one of the weakest in the game, so sitting 600 yards away from the Tiger you will have difficulty from any angle, unfortunately. If you can hit the lower hull without hitting the tracks or road wheels, that is where the armor is the thinnest (60mm vs. 80mm on the upper hull). Usually, though, I aim for the cross on the side, but I also close the range to -- well -- less than 600 (speaking of when I am in a T-34/76 -- haven't fought Tigers from a Sherman yet, but the guns are similar without HVAP).
So, close the distance (and hope his SA fails him) or bring a better gun if you are going Tiger hunting.