I just collected all of my courage and polished the hammer hooks. Wow. I had already polished the underside as well as the face of the sear and the grittyness was reduced, but still noticeable. After a few careful and weak strokes with 400 and 1000 grit sandpaper over the hammer hooks (sandpaper simply put around the magazine brake) I reassembled the gun and the dryfire is already promising. Together with a 13# hammer spring the trigger is already way better than stock (that had not been THAT bad).
If it wasn?t for the 75 Sport (SA only, professional trigger-job done, nearly a hair-trigger) I dryfired yesterday I?d estimate this as the beginning of a trigger becoming a good one. Even before taking out the bar and polishing it. The upper side of the bar looks neat as it is, but the cuts on the backside sure could need some work, currently showing deep machine marks.
A big thank you to all of you, namely schmeky and nothing for providing such well-founded how-to instructions! All I did today was achieved within 12 minutes, using only my leatherman - no punches, no hammers, no scratches on any part. It?s amazing how fast the unknown turns into routine as soon as you dare to touch it.