I’m in the process of replacing my clutch and brake cylinders. Mine is an early 1965 S1 FHC (30080) so the pedal box is different.
During my tenure of ownership, the brake pedal has always been higher than the clutch pedal There is about 2 3/4" of free play at the extreme end of the pedal before the rod contacts the master cylinder. There is no backstop adjustment for the brake pedal as I’ve seen in other threads on the subject; I have no qualms installing one if that’s what it takes.
I have it assembled on the bench with the brake pedal clocked on the splines in the same location as when I removed it.
At this point, I’m not sure what to do. Leave it as is? Re-clock the pedal? Add a stop bolt like the others I’ve seen?
My car is 30148 and has the stop plate you are referring to. I imagine yours had it at one time too. The plate plays an active part in adjusting the height and also prevents the brake arm from interfering with the semi-circular relief in the firewall. I also added some rubber to the stop plate to keep it from slamming.
I did not have the spacers on mine, although I noticed the un-threaded portion of the mounting studs was slightly larger. The is a uneven kink in mine - they probably bent it because they didn’t have the spacers.