Usually, no, there should be no problem. Just only use 2 3/4 shells.
However, there was some funny business with Remington and 20 ga “light contour” guns or ”LW” guns.
One thing about 870s though is the early 20 ga guns (and 1100s) were built on 12 ga receivers and later “LC” or “LW” barrels will not fit. The barrels may not be marked as lightweights though.
Since the barrel you are referring to is an express and has a 3” chamber, it is definitely a later one designed for the lighter scaled 20 ga receivers. You need to find out if your receiver is an early 12 ga type receiver or one of the later ones.