Valve Stem Seal Replacement
I replaced my M103 valve springs seals about 6 months ago using compressed air and an overhead type valve spring compressor. Everything went smooth. I used 100 psi air pressure. My compressor has a 20 or so gallon tank and it was cycling about every minute (lots of air). I wouldn't risk the possibility of dropping a valve by using the Scott bottle.
A couple tips:
1. When compressing the spring, give the collet a sharp rap with a small hammer to unwedge the keepers. If you don't do this the valve will start to open and your air will come rushing out.
2. Temporarily cover the oil drain holes around the valves so if you drop something it won't go inside the engine.
3. Use a small magnet to remove the keepers and the round shim between the valve stem and rocker (these are the parts that can get lost in the engine). A set of picks also comes in handy for maneuvering the keepers in and out of place.
4. Use prelube or heavy weight engine oil on the new valve guides and when reassembling the rocker parts.
5. I also brought each cylinder I was working on up to TDC so if I did drop a valve for some reason, it would hit the piston and not drop into the cylinder. This takes some care in doing because you have to turn the engine slightly beyond TDC, until the piston just begins to go down, and then hold the crankshaft with a good size socket braced against the garage floor. The socket keeps the engine from turning due to the air in the cylinder. Note that the direction of rotation of the crankshaft will tend to loosen the crankshaft nut, although the torque is not enough to actually do that.