I'm putting this master cylinder into my 86 Mustang GT. I gutted the stock prop valve and installed the adjustable one on pass. side. I used a line from the MMBAK3 kit to replace the rear cylinder line. My problem is the threads are different between my stock lines and the Cobra unit for the front. Do you sell a replacement line or adapter?
The kit you purchased is only good for an 87-93, as the description indicates. Going to rear disc on a 79-86 is actually quite simple. You only need to use an SVO master cylinder, LRS-2140E. No adapters required. It is a direct bolt on for 79-86 cars.
However, if you desire to keep your current 93 master, use MM-MMBAK17 for a problem free adaptation.