Leeds/Bradford - two separate cities, one of whom independently went for the city of culture.
Newcastle/gateshead do work together closely - then again they are separated by around 500 yards of Water as opposed to the 20 miles between Preston and Blackburn.
But please feel free to persue this avenue - nothing would please me more than seeing the only way for you lot and PNE to survive is an unholy alliance - though of course home games would be played at deepdale, with it being the oldest pro sports ground in the world