They don't come in Singlecoil form, so if you're really going to equip the Strat with them you will need to enlargen the cavities. I'd recommend you to see a luthier however if you never done this job before; you could easily damage the body beyond fixable.
You could also just save money and time and equip the Les Paul with PKs, changing pickups is not a hard job and with a soldering iron and a little bit of internet research you can do it yourself, also if you don't like the result (which I believe you will since BKPs blow you away when you hear them the first time) you can always put the stock pickups back in.
Another thing to consider would be body woods, and what exact kind of "Djent" you're going to play; just because the description says that the Painkiller is the ultimate "Djent" humbucker, doesn't mean all the other BKPs can't do it as well or even better considering your guitar specs and other styles you might wanna play. The Aftermath and the Blackhawk are two other pickups Misha from Periphery and folks alike adore for "Djent" if that is what you're looking for.
Hope that helps a bit;
Cheers!
