I've had a pair on the rear of the mini K for many years - no problems but don't drive fast enough to notice any real difference.
It is up to you. The Superfins are about 3 times the price of cast iron ones but look pretty.
Checked the width of the insert on a pair of Superfins. Comes to 38mm which is very close to the width of the front brake shoes before the friction material of the shoes run over the alloy parts of the drum. Don't really know whether that will be a problem.
Attachment:
Super Minifin drum.jpg
The cast iron drums are a fair bit wider at 48mm.
Attachment:
Cast iron drum.jpg