I don't have any stock pickups to hand, but from what I remember they're alnico V, with DC resistance about 5.9k and 6.5ish on the bridge. Any of the BKP vintage range (with the exception of Apaches, as they're alnico 3) are fairly close in terms of spec.
The biggest difference is in the way BKPs are made, though - handwound as opposed to machine wound, even pickups with exactly the same measured specs will sound different because of the differences in manufacturing methods. FWIW I've swapped out both my strats with BKPs (one 59 set, one 63) and they're both fantastic, with noticeable improvements in dynamics and warmth.