To make a long story short, volume is the key. Crank your amp.
To make a short story long...
Old-style Strat pickups need to be played loud and hard in order to break up like you are probably used to from those MIM pickups. And a lot of that has not only to do with output, but tonality. The pickups don't inherently have a very strong midrange, so they seem "smaller" than high output pickups to your amp. But when they do break up just right, there is nothing like them. Their inherent cleanliness is actually their biggest strength once you start overdriving the amp. People think of Hendrix as an example of how Strats sound when overdriving an amp, but remember what volumes he played at to get Strats sounding that way. Also, listen to the albums, and you'll see right away that he used clean Strat tones quite a lot, so there is plenty of room for clean Strat tones even in heavy music.
As for pickup height, I'd start at the recommended factory settings and work from there. For old-style Strat pickups, that's 2.4mm low side and 2mm high side. Drill bits work well for making these measurements. (I use mini screwdrivers with marked diameters.) The bridge will sound thin, but that's the point IMO. Pump that baby through a cranked amp and you'll see the benefit of having it be that thin. Razor blade distortion like nothing else.
Also, try the 2nd switch position (B+M) with the farthest tone control rolled all the way down. Or, if your Strat has modern wiring, you can just use the 1st position (B) with that tone rolled all the way down. Instant hair on the tone by doing that. You can also rig the guitar with a lever or push/pull switch that will put the bridge and middle pickups in series for a 12-13K pickup. That swallows up a lot of that super present high end and gives you a healthy amount of high output midrangeyness to drive the amp.