why does the over center spring have to be removed

If you have a diaphragm clutch, remove it. Period.
You wont have that hitch, or over center,feeling when you press the clutch in.
Much smoother without the spring.
Nobody uses the borg warner clutch anymore anyways.
Remove it, and chuck it as far as you can.
Or put it on ebay for something like $350.00 :)