Don't know if this is proper but these resources are great:
http://www.matthewsvolvosite.com/volvo-850-repairs.

This is the one I used
http://www.matthewsvolvosite.com/plan-for-in-car-valve-stem-seals-replacement.html


https://sites.google.com/site/incarvalvestemsealreplacement/


My learnings are:
1. Use a compressor with spark plug adapter. (not the rope trick) Comes with tool below.
2. Get the universal valve tool. Lessor expensive ones can be found on Amazon. CTA 2235 worked great.
3. This tool will be used pushing handle with cheater bar, up on exhaust valves and then down on the intake ones. Not enough clearance at fire wall to push down.
3. To free the keepers from top spring plats, tap the plate with drift 1st to free them up. If not, the valve keepers will not break free when compressed and the valve with go down and releasing compressed air.
4. Take your time, your back will be stressed.
5. Use a flat head driver magnetized to help keep those keepers on. I always put them on from the passenger side, and then slid them around the stem to do the next one.
6. Get a seal puller! I used a surgical clamp pliers. Wiggle the seals and slower they pop off. Some bits may break off, go slow.
7. COVER all HOLES!!!! I lost one keeper but fished it out with magnet antenna. My heart stopped!!!!!!

Rob