I am not sure which model your pump is, but the Gas Pump Blue Book lists that the Model 610 was manufactured from 7-18-27 to 5-2-30 and SN ranged from 240,931 to 355,219 for those years.
If it is a Model 625 the Blue lists that model was manufactured from 11-28-27 through 2-11-36 and SN ranged from 257,537 to 450,039 during that span.
It also lists in 1931, the SN ranged from 385,918 to 413,552. If you make the assumption that equal numbers of pumps were produced in each of those months, you should be in the ball park, but maybe not the exact seat your pump was built.
Hope that helps. Neil