9" vs 10" brakes

Working on a 70 Dart
has 9" brakes
started out getting rid of the left hand studs
by taking the drum off a 71
found out its a 10"

Can I just change the backing plates etc
or do I need to change the spindle also

Can also take everything off the 71
(due to changing it to BBP disc)

the rear is also from the 71
8 3/4 with 10" brakes
we put it in the 70
would I need to get the proportioning valve too

Thanks,
Howard and Gayle