I was told by an experienced machinst that the "old" "original" "minilites" do not take to being machined!
I was going to do this very project on an original set from someone here on the board. They were 6.5x15s
Made in England. Back around the mid 70s.
He stated that he had tried to do exactly what you are considering and that the old original castings were very pourous and did not machine very well. Leading to possible weakness at the area of machining.
He strongly suggested I find another way to adapt those wheels to work for me.
I know folks have had success with machining the "newer" versions from Panasport.