Reader Fenris suggests that if I am interested in black-white differences in sexual dimorphism, I shouldn't look at indirect measure like life expectancy, but should investigate height differences. I thought I had done it previously, but turns out that it was blacks and Asians that I compared before.
To make the best comparison, it makes sense to look at populations with environments that are as equal as possible. How about young blacks and whites measured recently? In fact, the data indicate that racial differences have reversed in the U.S. over time. I used Fenris' source and also found a newer one.
Here is the black sex difference in height minus the white sex difference for different age groups and periods:
Ages 40-59 (1988-94) -1.4 cm
Ages 20-39 (1988-94) -.2 cm
Ages 20-39 (2003-06) +.7 cm
As conditions have improved for blacks, their sexual height difference has changed from being smaller than that of whites to becoming larger.