Based on thousands of people who took both the SAT and GRE in the 1980s, we can say that a verbal GRE of 510.1 (SD 107.7) equaled an SAT verbal of 518.8 (SD 104.7)

gredata

By the end of the 1980s, the average GRE taker 484 SD 125 (source)

From the above data points, we can say GRE takers had the equivalent of a verbal SAT of 493 (SD 122).

Now national norms studies suggest that if all American young adults had taken the SAT in the 1980s (not just the college-bound elite), the verbal mean and SD respectively would be 376 and 102 (Herrnstein & Murray 1994). If the U.S. mean is defined as 100 and 15 respectively, this puts the 1980s GRE population at 117 and 18.

[UPDATE July 25, 2024: A commenter suggested that the strangely high standard deviation of the GRE takers was inflated by the uneven verbal scores of foreign test takers. I thus re-did the analysis using the math SAT and this time I got a slightly lower mean IQ (116) but oddly an even bigger SD (19). ]