There were plenty of inline 4 rear engines cars too, like Simca 1000, Renault 4CV, Renault 8, Fiat 600, Fiat 850.
Some were water cooled too.
Advantage in early RR cars (in Automation) is the better brake performance (more balanced with small and inefficient drum brakes).
They are lighter compared to the more conventional FR layout because they don’t have the transmission shaft. For the same reason they should have a bit more cabin space too.