I agree getting that mainspring housing assembly back together is a pain, but why would you have to? I have never seen a Ruger .22 auto hammer spring weaken and the mainspring housing assembly is supposed to be a permanent assembly.
To get the spring plunger, spring and detent ball back in, you have to grip the bottom of the latch in the side of the vise jaw, long side up, then push the other parts in over it with the back of the latch in its slot in the back of the housing. It is not easy, and you need to have some means of catching parts if they fly. It is easier if you have someone else with a punch ready to put it in the lower pin hole when they line up.
I only ever had to reassemble one and that was because the owner decided to take everything apart for the fun of it, then couldn't get things back together. That guy was a real PITA, even though I made money off him.
Jim