Get it from rock auto man that’s what I did. Got both my 93 MC and Booster from them, then tried to paint my booster. As you can see the booster size is a huge difference and took some work to get it in there but it’s doable.
In the meantime, you really need to change the MC and get the proper MC on the car. You can bleed them all you want but you will always have a soft pedal as the stock MC bore is too small to push enough fluid to properly operate 4-wheel disks. You are probably putting the pedal to the floor and not getting a whole lot of response from the system.
You can delay on the booster, but i'd considered the MC and supporting mods necessary at this point.
That booster is the right one but that MC should be one of these with or w/o the reservoir but that’s bc I went with the big cobra brake conversion so that might be the right one for your setup, I bought the one with res. Listen to all these guys man they were are big and great help, and got me through my swap. @Mustang5L5 would be better to answer that question for the MC for your conversion.
For his setup, (rear SN95 disks with the 94-98 GT/V6 front setup with single 66mm piston caliper) he wants a 94-95 GT Master Cylinder.
He can also go with a 1993 Cobra Master Cylinder which would be a slightly softer pedal with more travel, but still work. I'd recommend this one if you decide to not change out the booster.
Reseviour or no reseviour all depends on if he wants to pull his out and swap it over. I personally find it a PITA
Both MC's use the same exact 3-2 conversion kit from max motorsports.