This is another common "mod" I do a lot. Taking out standard factory pick ups and swapping them for aftermarket ones. Some companies make OK factory pick ups but most of the "big brand" guitars have pretty average pick ups from the factory. That's one of the reasons there are SO MANY aftermarket and "boutique" pick up makers around.
This is a pretty simple job on a Strat as they were designed around easy and cheap assembly which (generally) means easy repairs for simple things like this.
The original pick ups were being replaced with a Seymour Duncan rail for the bridge and two Fender noiseless pick ups. The rail is a humnbucker in a single coil size with blade (or rail) magnets instead of pole pieces. Being that they're the original single coil size, there's no modding or routing to be done. They drop straight in.
There's heaps of great choices for aftermarket pick ups on the market now. I personally recommend a grumpy guy in Adelaide called Brierley pick ups. His work is great, his prices are cheap and I have yet to fit a pick up of his that doesn't make me smile. Like mI say, there's plenty out there so do some research and see what suits you best.
Because most modern Fenders are routed for several different combinations of pick ups to save on assembly time and cost, you could fit full humbuckers or P-90's to the bridge and neck positions with only a need for a new (or cut up the original) scratchplate.
With the new pick ups in and wired up it was a simple matter of a set up and we're away.
Being essentially a "brand new" guitar it needed some attention to get it playing nicely. Most guitars come from the factory needing some degree of "expert" setting up to get them closer to playing the way they should. These guitars generally come "close" to playing OK, but with a little love, the transformation can be amazing.
The truss rod needed some serious attention and after a quick fret dress the neck looked good. The nut was high as per most factory set ups so that was brought down a little and then the action and intonation set.
All in all it was a simple job that makes a new "average" Strat into a much better playing and sounding instrument for very little cost.
The trick with blending any set up with humbucker and single coils in the same guitar is balancing out the volumes of HB to single. This will always be a slight compromise as generally speaking, the HB will be more powerful (and louder) than the singles.