No doubt that C4C5 and Chick have had way more experience with this, but for a fellow that pushes paper all day, I have had my fair share of SBC valve stem seal replacment (on the car!).
Most shops will go ahead and suggest a complete valve job to just plain do it right and avoid other problems. However, if you are as stubborn as me and have the extra time, and talent it can be done on the car.
Let me tell you though, this is a pain in the butt job for anybody much less the shade tree mechanic. Here is why, not only do you have to pull the valve covers off, but you have to work in that tiny cramped space to pull the spark plugs, screw in a air line fitting (built mine from a spark plug anti fouler kit, 2' of hard air line and quick snap fittings) one cylinder at a time, pump the cylinder with air pressure, remove the rocker arm, get your valve spring compressor down in that tight space, compress the valve spring, remove the tiny retainer clips on the valve stems, pull the valve spring, clean and remove the old o-ring seal, pop the new perfect circle style seal on, tap it into place, then reinstall the spring, retainers, rocker arm, and spark plug.
When it is all done, you have to go back and cold set, or warm set (whatever you prefer) the valve adjustment and then seal the engine back up. This is a good time to recondition your valve covers, replace spark plugs and wires.
I have done it on four C4s, two S-10s 9one with a V8 and one wiht a V6), and one Gen III camaro all in the car. I hate doing it, but it is well worth it to not see that huge embarrasing puff when you crank it up. It was really bad with my Convertible vette having to choke on that cloud of smoke in front of the whole world when the top was down.
Just kidding. Mine did that too. 
