The Arnott blower is very simple indeed, it just has 4 Tuffnol blades that are held against the blower wall by centrifugal force. As long as the blades are a good fit in the rotor slots, the bearings at either end are good and it has a small constant loss oil supply it can't really go wrong.
There is a lot of good info here.
https://www.mg-cars.org.uk/mgtd/mgtd_acc...argers.htm
There is a lot of good info here.
https://www.mg-cars.org.uk/mgtd/mgtd_acc...argers.htm