One thing to consider when purchasing 1969-70 brake boosters is that the assemblies do not interchange. The push rod is the determining factor. mis-matched boosters and pedals will cause diaphragm failure fairly quickly. It is not uncommon for sellers to identify the assembled boosters incorrectly, or say that they fit 1969 and 1970..
Lollipop shaped end on 1970 boosters.
Closed "J" on 1969 boosters.