The bolt stop on an Argentine 1909 protrudes out a little when the bolt is closed, what's the best way to modify it so it's uniform?

That is often a worn or weak bolt stop spring. Sometimes you can grind off a little from the L-shaped foot at the rear of the spring to allow it to draw closer to the bolt stop stud cam. This applies more force on the spring and helps close the bolt stop. Failing that a new spring may be in order. www.springfieldsporters.com carries this part and they may even have new, unissued ones.