I'm not talking about a Strat sized P90, but an actual P90. $$$a P90 in single coiled sized pickup just won't sound like a full P90s.
What you gain, you will loose any stratiness...
Plus it doesn't blend well with the other strat pickups..
If you have a tone control for your bridge,
I've had success with the Harmonic design super 90.
you will need a tone control for it.
but it's NOT a p90, nor a humbucker.
I ended up taking it out of my strat...
now thinking about routing my strat bridge for a real P90 or Humbucker...
I have a parts strat with Lollar P90s, a USACG conversion neck (24 3/4") with a 12" radius, alder body. It's my go to for Beatles tunes. Were I to do it again, I would get an 11" radius fb instead. I lose track, but I think I have a Gotoh two point bridge in it.
Here's a prettier one than mine...with three pickups.
fwiw, that Chandler body came routed P90 S P90 back in the late 80's, so I didn't have to deal with routing.