If you have a 70 style front disc setup, it used a 1" bore master

The 73 style discs used a 15/16" bore manual or a 1 1/32" bore power M/C.

If you were putting a 73 style disc setup in the 70, just use the complete 73 setup in front.

They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.