Frustration!

After a few days figuring out how to fit the new drive flanges for the gearbox, I made this flange spring compressor out of B&Q metal bits and threaded rods so that I could drive the flange in far enough to refit the circlip over the end of the shaft.  It was all too tight when I finally succeeded, as it turned out the new flanges have 3mm more depth on the internal shoulder.
Did I get the wrong part number, or do I have to machine-off the difference?