68 Charger multiple brake issues

[Kern Dog]

Originally power drum all around.
Converted to disc front drum rear by shop. Wilwood front disc with master cylinder. New drums in rear.
Thanks to a member here I see I have an A Body booster with a stand-off from firewall. See pic.
Brakes terrible so I started investigating and found Residual Valve in backwards.
I then pulled master cylinder to check rod length. Rod at least 1/8 long. With it adjusted all the way in.
So here is my questions: Can the A body booster be used?
With master cylinder removed I lightly pressed brake pedal and felt a spring tension on pedal, is this normal ?
Summit does list the A body style with firewall stand-off bracket for B body.
Hopefully it can be used because repiping the master and proportional might be beyond my scope due to access.
Thanks

Personally FWIW I would install a 15/16 manual master cylinder and toss the booster.

I disagree. A manual master cylinder B body takes more pedal effort than a properly equipped power boosted system.

Or a hydroboost if you really want to stop well

In theory, hydroboost is an excellent system. Most report that their brakes are a bit touchy though due to the high amount of boost associated with the system.

How did the linkage going to the brake pedal work out for you, did you have any length issues at all? Thats not a bad price, and it comes with the correct plate. I have an all-wheel disc setup in my 67 Charger, and the pedal is spongey, I'm wondering if it's just the M/C and booster combo they used.

It seems that all of the systems that have a standoff mounting design are that way because they have reduction linkage between the booster and firewall. Manual systems have a single pushrod from the pedal to the master cylinder. Vacuum/Power systems reduce the pedal ratio since the assist makes braking so much easier. I have not measured out the difference in pedal ratio between manual and power but I can say that I have not seen anyone correctly state the manual ratio. Rick Ehrenberg mentioned a couple of times that manual is 4 to 1 and power is 2.5 to 1 but he is way off....which disappoints me since he is usually sharp as a tack. If you do the math and measure the entire brake pedal arm and all points, the number comes in well over 6 to 1. Measuring the power system involves computing the shorter lever arms and "locomotive" type linkage pieces. I have not been curious enough yet to delve into the numbers of it.
Stock 1966-70 B bodies had the master cylinder and booster bolted directly to the firewall and the reduction linkage was under the dash, inside the car. Maybe it is cheaper and easier for these companies to make generic boosters with standoff bracketry with reduction linkage to fit multiple applications.
I struggled for years trying to optimize my braking system and it wasn't until I swapped in a stock type 66-70 power booster that I finally made significant progress.