According to the bikehistory site, (with the digitized Schwinn catalogs), Schwinn built the Racer in 1933 and 1938 as a true racing style bicycle, then reintroduced the name in 1957 as the upright seated classic we have been discussing here. I haven't personally seen any examples of configurations other than 3 speed with rim brakes, but according to the sales catalogs, they were also sold with single speed coaster hubs, and with Bendix 2 speed Automatic aka "kickback" hubs until at least the mid 60s. The Racer's last year is shown as 1971. https://bikehistory.org/bikes/racer/
The Speedster was introduced in 1959, with single, 2 and 3 speed hubs and was offered through 1978, but had quite a lot of metamorphosis over its history.
- From 1959 -'62 it was a cantilever frame
- '63 until '71 it seems that the Speedster was only offered in the "camelback" style, with reduced frame height for youthful riders. There were 24" and even 20" Speedster models.
- It wasn't until 1972 that the full sized, diamond frames seem to have been offered.
Vintage Schwinn Speedsters were made from 1954 to 1978. This page shows images and text from old catalogs of this classic bicycle.
So, this reinforces your idea that the Speedster took over the market slot of the Racer when that model was discontinued in 1971. Perhaps even the same frame design was used? It would be interesting if someone would compare a 1971 Racer to a 1972 Speedster.