hey guys, i gave it another shot today, with much better results. i first tried using a valve spring compressor that i had. what a pos, the thing actually came apart while i was using it. so i scrapped that and tried the 32600 tool again. And this time, I made sure that the valves could not move at all, by stuffing a microfiber towel underneath the valve/cylinder i was working on. The same thing was happening again--only one keeper slipped onto the valve, while the other went on only partially. so what i did was position the tool right on the keeper that stuck out, gave it a good whack, and it went on completely as well. I did this with success on 3 different valves, doing them over multiple times just for fun. as long as one keeper is in well, and one is partially on the valve, then no need to remove both keepers and install again--just place the 32600 tool on the keeper that's partially on, give it a good whack, and both keepers will be on the valve properly. awesome!
the key, i noticed, is to prevent the valve from moving at all. the few mm of movement that the valves had yesterday when i was trying the 32600 tool out made it impossible to get the keepers on. but if the valve is completely shut and immobile, that gives the keepers just enough height to slip onto the valve stem up top, with the 32600 and a good whack of a hammer (i used a 3 lb drill hammer). i even got both keepers to slip onto the valve stem perfectly with just a single whack, a few times. again, the key is to prevent the valves from moving at all. makes me think the rope method of installing springs/retainers might not be the better solution after all, unless you have a really good valve spring compressor tool: one that can compress the spring to the point where you can slip the valve through the spring/retainers just enough for you to stick the keepers on the stem, after which you can release the spring tension on the compressor so that the retainer makes its way back up to surround the keepers.
edit: if the keepers look like this, you can still place the 32600 tool on the keeper that's sticking out, and whack it down into place with the 32600 tool and hammer: