There was an article in "Rifle" magazine on how to make the 788 trigger adjustable and the 581 trigger system is similar. It was quite a while ago, probably in the 1980s, but it might be possible to find it on the Internet.
The procedure involved drilling and tapping two holes in the trigger housing, and cutting the spring that provides tension to both the trigger and the sear. I did a couple of them "way back when" and they worked quite well.