Can confirm what the other poster said, very different. In addition, a humbucker with a coil split doesn't really sound like a single coil generally (there are some things you can do to get closer, but we're only talking about raw pickups with no mods here).

It all has to do with the windings and the fact that the magnets aren't interacting the same way. A fender Texas Special bridge single coil is about 6.56k ohms impedance. The Shawbucker 2 is about 7.8k ohms. So humbuckers today aren't really just two single coils flipped and stacked. I don't know enough of my history to say whether that's how they started, but if someone were to claim that I would totally believe it.