Thanks everyone. I think this gives me the right plan:
- stuff cylinder with rope to keep from losing valve
- remove broken spring with tool I need to buy
- Inspect spring further for evidence of cause
- remove other spring on same cylinder to measure pushrod and buy replacement
- confirm new spring and rod are exact matches
- install
- change
oil and filter
- cross fingers
- crank motor
- check compression
- look listen learn
- let it start