There are 8 holes in the firewall for the pedal assembly / power brake unit. I am not sure if all are used.
I am not sure if I should mount the pedals assembly first and the power brake unit after of mount the power brake in a way that it retains the pedals assembly
Can somebody explain or send pictures?
Many thanks
they mount differently depending if you have power or manual brakes , the brace mount up to the cowl & through the firewall & the pedals mount to the brace
Here is a picture of the brace that Neil mentioned.
https://www.summitracing.com/int/parts/sum-760201/overview/year/1971/make/plymouth/model/cuda
Found this video that might help you. It's a bit annoying but explains it.
The four yellow ovals in your picture are for power brakes, four green standard brakes.
I usually mount the pedals first, using an awl to keep the firewall holes lined up while I tighten the pedals.
Another tip is to put the power brake lever system on the booster first before fitting it on to the firewall.
Peddles first.