Power to Manual conversion questions

The firewall plate shown in post 6 is probably a B-body only thing. My 64 & 65 A-bodies mount the MC directly on the firewall, as does the power brake stand-off brackets. My 1965 C-body has such a plate. Perhaps they list for A-body for somebody repairing rust damage.

You can probably use the same MC. Check rockauto. For most years, the manual and power MC's had the same bore ID. When they differ, the power MC often has a SMALLER bore. Why? Consider the lever arm ratio in the stand-off brackets. You can probably bend your existing tubes to fit the MC directly on the firewall. You will need a manual rod to the pedal. Many manual MC's come w/ a brake rod, at least for my years (see rock).

But, if you don't mind resto-mod, you can buy a new booster w/ brackets and MC for ~$140 on ebay. Most look like a GM style booster that can probably be replaced easy in the future.