Sorry can't help you! Glad you posted this question. I'm betting the Shelby
booster was no different than regular Mustang. Also most auto parts stores list
both the Bendix and the Midland booster for vintage Mustang. If you try to
order a Midland you find the rebuilder has no Midland cores to rebuild. They
try to sell you a Bendix or in some cases you can send your Midland in and get it rebuilt.
An afterthought. My '68 Mustang and '70 Torino both have power disc brakes. They
both have the original vacuum booster. Both are Midland. Doesn't prove anything
but I suspect the Bendix was/is a replacement.
I have a 69 GT 500,
a 70 Q code drag pak Dearborn car
a 70 Twister Special, Dearborn car
they all have Bendix on them. My H code 69 Mach 1 has manual drum brakes.
I'm the person that traded 69 Boss 302 dizzy with you.