Thanks to those that answered.
The spring on the sear is another matter. The one I asked abut above seems to be the hammer spring. guntalk-online.com doesn't show either of them nor does the Ruger parts breakdown. I can honestly say that I have worked on mini guns in a helicopter, rebuilt rotor systems to .001 tolerances, rebuilt turbine engines to unbelievable minute tolerances, but have never come across anything that once apart looks as though each successive part was an afterthought. My praises about Ruger have taken a severe downward spiral.
A HOUR LATER.
Finally got it back together. Only one part left over. It is the small ball like item that fits into the spring at the front end on the bolt stop release (not shown on the Ruger parts breakdown). Seems to work OK without it so I'll see what happens at the range.