Here's my thought...
NBA/ABA split
Now, we're going to take some liberties here because we don't have a perfect 10 and 10 of each, but here's how it would break down:
NBAWESTChicago
Phoenix
Portland
Sacramento
Seattle
EASTAtlanta
Cleveland
Orlando
Toronto
Washington
ABAWESTGolden State (ABA roots - Oakland Oaks)
Houston Rockets (ABA roots - Houston Mavericks; became well-known ABA teams Carolina Cougars and St. Louis Spirits)
Los Angeles Clippers (ABA roots - Los Angeles Stars)
San Antonio Spurs (ABA roots - San Antonio Spurs)
Utah Swarm (ABA roots - Utah Stars)
EASTIndiana Pacers (ABA roots - Indiana Pacers)
Memphis Grizzlies (ABA roots - Memphis Tams)
Miami Heat (ABA roots - Miami Floridians)
Minnesota Timberwolves (ABA roots - Minnesota Muskies)
New Orleans Jazz (ABA roots - New Orleans Buccaneers)
As you can see, some liberties were taken with the ABA teams. Just because there were ABA "roots" doesn't mean that ABA team became the NBA team. Just that the city once hosted an ABA team.