FYI,
there was no plastic spacer on manual brake cars.
master cylinder bolts directly to the firewall plate with a white foam gasket between them
As far as I know there was always a steel reinforcement plate installed between the master cylinder and the firewall on manual brake cars. I know my 1972 B-body has one.
There was always a steel re-reinforcement plate behind either the booster or master cylinder. Be it manual or power brakes - drum or disc ( plates were different for each individual application.)
The only 'spacer ' was on power drum brake applications. Even then it was a combination of plastic and aluminum.
