I have a 71 EC with drums on rear, discs on front, I'm told the diafram has a hole in it. Is it possible to rebuild or just change the diafram

Ken,

Those boosters can be rebuilt - check out Booster Dewey

Power Brake
4533 South E. Div. St.
Portland, Ore 97206

Don't have the phone number available here.

Also pick up a copy of Hemmings Motor News - plenty of places advertised there for rebuild services. Rebulid without CAD plating should run less then 100.00.

Hope this helps.

Rich