This^^^^No, they absolutely don't sound like a P90 when splitted. Also not like a "common" singlecoil pickup. A P-90 has other characteristics.
The Duncan P-Rail indeed is a great pickup you could/should try out. Another pickup sounding like a P-90 would be a Bluesbucker from Dimarzio's line-up!
Did you already adjust the pickup-height?
classics work at the neck or middle...i a classsic and a plus as a middle pup on two 3 pup models....How would a classic 57 work at the neck with Burstbucker at btidge ?
Or soxuld I go P rail ?