Manual-to-Power Brake conversion issues!

i have a 1974 plymouth duster that i am currently restoring, this was a factory manual brake car, but i am now converting it to power brakes. i have purchased the Wilwood Dynalite Drilled and Slotted brake kit for both front and rear. my problem i am having is that i have purchased a cardone rebuild power booster from advanced auto parts. i have searched many auto parts and advanced was the only one who could get the reman, everyone else wanted to send mine out which is an issue because i never had an original power booster. upon receiving this cardone i noteced the the lenght and width of the studs that bolt on to the firewall is much different than the length amd width of the factory holes drilled in my firewall. what is strange is that the studs on the master cylinder side of booster are spaced coorectly and my factory master cylinder fits right on. at first i assumed i have received the wrong booster, but it looks identical to the factory style boosters that were put on dusters. with a little research i noiced on a SSBC Power Booster/Master cylinder combo that their was a bracket that came off of the firewall and to the back of the power booster to adapt the wrong stud size, this looks kind of stupid but i would like to know how the factory did it and if this adapter bracket is a factory item. if anyone can help me with this issue that would be great, if this is a factory braket and u would like to sell it please pm me because my resto is at a stand still! any info will be much appreciated Thanks!