Power Disc Brake Master Cylinder to Manuel setup

No plate at the firewall, unless you're adapting the late master cylinder. No pushrod on power brakes, the offset linkage bolts directly to the pedal- the booster has a rod that pushes the master cylinder.
So, since you are removing the booster (and linkage) you need a pushrod. #4.
So on the 74 duster I have with the power booster once I removed that I don't need the big steel plate like was on my 66 satellite behind the manual master cylinder?