I know of no good way to recover the incomes of property owners, but we can get a flavor of the distribution of income among beneficiaries of rent stabilized properties in Los Angeles, by looking at the income distribution of those who live in properties built just before rent stabilization and just after. We can't exactly nail it, because rent stabilization in LA went into effect into effect in October 1978, and the census tells us the decade in when properties were being built. Still, comparing the incomes of renters living in buildings built in the 1970s with those of the 1980s can tell us something about how well targeted rent stabilization is.
I downloaded American Community Survey data from IPUMS USA. (See Steven Ruggles, Katie Genadek, Ronald Goeken, Josiah Grover, and Matthew Sobek. Integrated Public Use Microdata Series: Version 7.0 [dataset]. Minneapolis, MN: University of Minnesota, 2017.
https://doi.org/10.18128/D010.V7.0). I looked at the city of Los Angeles, and stripped out single family detached houses, and, of course, owner houses. I used the ACS Household Weights. Here are the income distributions I found for properties built in the 1970s and 1980s.