I'm not sure about the regular strat sized hb's, but I get amazing quack tones from my strat with an SM1 in the neck, and a classic stack in the middle. I think if you went with just about anything except the hot rails you would still get pretty good quack, but you definitely will have to play with the pickup heights a bit to get the best sound.
i use 2 single coil sized humbuckers (duckbucker neck, JB jr bridge) on my strat with a pu off an ealy 70's strat. i can still achieve the quack by either using only the mid pu or combining it with the neck pickup but as mentioned by kyuss you loose about half a duck.
im acually debating at this very moment weather or not to wire my 2 buckers as singles as well as install toggle switches to change them back and forth but im not sure if i will get a true single coil sound from it or not. if anyone knows this answer they could let me in on this info it would be greatly appreciated...
what is the roundest SC sized humbucker with the lowest output? i was thinking of maybe throwing a quarter pounder in the middle to even out the output issue. with the bridge humbucker being pretty hot i dont usually use the number 4 position too much but the nice quacky number 2 is something i really dont feel like losing.