there is an "always on top" post about coolant on this site, the G Pence write up is it.
https://pantera.infopop.cc/top...-cooling-system-info
this set coolant arangement was also recomended by a guy name Carrol Smith, (racer/engineer/author)
I also found technical papers from 1940's for similiar arrangements saying the swirl remove entrained gases from coolant