Like many if not most pickups, vintage P-90s were not overwound, and in many cases the "underwound" versions of today are about the same as the stock vintage winds. So yes, an underwound P-90 will sound like a P-90. The CP JM pickup is what I just put in a Strat bridge position, and I consider it to be a P-90 more than a JM, though it's not exactly a P-90. My reason for choosing them was they are F spaced and line up with the strings near the bridge. For a neck position I'd choose a true P-90, but OTOH the CP JMs come up used for cheap because that guitar is often bought by fans of vintage JMs who don't want the P-90 sound. Not sure you can buy them new, but there are lots of J Mascis Squier JM pups for sale used, pretty similar P-90 with bar mags and pole screws plus a base plate, seem to have a good rep but never tried one. Very tempted by the J Mascis JM Squiers though.