4-plexes aren't as great to convert in Austin because they're often way outdated and old. If you're going to convert, you'd want to choose a small apartment complex or duplex. Apartment complexes are tough bets in Austin because there's so much competition for them. There's also so many conversions that have taken place ,especially in Central Austin, that there's been a glut.
Some investor specialists do conversions, but there's no one company who specializes. Julie Alexander's company specializes in condo conversions on the legal side, so she will have references. They do about 80% of the condo conversion docs in town and are the closest thing to a "specialist" out there. AustinCondoLaw.com is her site I believe.