You can still make them fit, you just either have to mount them using Gibson-style threaded inserts and bolts, or you have to live with the screws sticking out the back of the vibrato spring route a little bit.
If you want hum-cancelling P-90s that will fit in a normal P-90 route properly without worrying about the screws at all, hit up The Creamery or Catswhisker pickups. They're both cheaper than Kinman and though they don't make a hum-cancelling P-90 that sounds like a P-90 as a standard model, they can both knock you up a hum-cancelling pickup with original P-90 tone if you drop them a line and let them know what it is you're after. There's also the recent Gibson Sidewinder P-90, though they're a bit hard to find as aftermarket part.
And you know, if you really want to avoid the vibrato spring rout, you can always just order a body with a fixed bridge.