Boy, I've really messed you up now!
What you had originally is correct (2.525") which is th same as the Sherman. What you have NOW is too long and would describe the situation I THOUGHT you had before Wheeeeeew! 2.540" would be way too long! Anyway, I think you will discover there isn't anymore you can do with a .270 case that will improve it over the Sherman. You can't take anymore taper out and have extraction. You could play with the body/neck length a little, but would end up a wash. The Sherman has a .300" neck. You could add a little more body length and a shorter neck which would give you 5 fps and a short neck
......Rich