Portland and Indianapolis were to be an improvement on the Northampton class cruisers. However, the USN decided to abandon unit machinery and go for more heavy protection. So the ships of the Portland class that were to be built in Navy Yards were changed to the new design, becoming the New Orleans class. Portland and Indianapolis however were laid down at private yards, (Bethlehem, Quincy, and New York Shipbuilding, Camden respectively) and the Navy would have to pay a penalty if the design were changed. Hence the two-ship class. The Portlands were also designed as Fleet Flagships, and when Spruance was in charge of the 5th Fleet, he frequently flew his flag on Indianapolis.
Had Indianapolis survived the war, she very likely would have been used as her sister was. Portland went to the Atlantic for Magic Carpet service, and was badly damaged by a hurricane on her second homeward run. Three soldiers were killed, and a number suffered injuries, including spine fractures and paralysis. She was declared not seaworthy when she reached New York and was surveyed. Still, she went into mothballs, and wasn't struck from the Navy List until 1 March 1959, and sold for scrap on 6 October 1959.
Assuming Indianapolis is on a different Magic Carpet schedule, she won't have the hurricane problem, and will make a number of runs. She'll go into reserve as all pre-war heavy cruisers did, and she'll be stricken and sold for scrap in 1959 as well.
My thoughts,