You've got two different sorts of pickups. Also you could have different magnet types and different wire gauges. The DC resistance value doesn't tell you much unless you know more details about the pickups, so I wouldn't go by it at all in this instance.
But most mixed pickup designs put a humbucker in the bridge and a P90 in the neck e.g. the Gibson BFG. It's a good combination.
You can see from the picture that a soapbar P90 is longer (pole to pole) than a humbucker (about as long as the humbucker + the pickup ring) and also narrower, so you'll end up with a gap at either side. You either live with the gap, or you return the P90 and go for a humbucker sized P-90. A dog-ear P90 has a cover that just about covers up a standard width humbucker hole. You may have to fill the ends of the rout with some wood in order to fit the mounting screws, but that won't be seen. You'd need to get a proper neck-position dog-ear P90 as it has a lower cover than a bridge one. They aren't height adjustable, but a neck one will be the right height for a LP style neck position.
Can you provide links to the pickups you've ordered?