I need your opinion
My 66 has a single master cylinder which I like to replace it with a dual for safety, my questions are;
since the dual din't came on the 66 the master cylinder on the 67 will fit?
shoul I go to the expense of installing a brake booster also or the dual master cylinder alone s OK ?
Thank you

 

The 67 will fit. If you install an original style booster it will require pedal modification.

 

You should be able to get a power brake conversion kit that will include a dual master cylinder and a brake booster. If you do a search on Mustang Monthly, you should be able to find a tech article describing the procedure. There may be one in the tech section here as well; I haven't looked though. The kits can be found at lots of classic Mustang parts houses. By the way, this conversion should be much cheaper than converting to disc brakes. I can get the parts locally for under $300; I don't know what they run at the various internet parts houses.

While the dua master cylinder offers some safety against brake failure, I would definitely go ahead and add the power booster while I was at it, as this should provide noticeably better braking.

 

Sorry..I forgot to mention that I already have disck brakes on the front (rear drums)

 

Most folks go ahead and add the dual master cylinder as a part of the conversion to disks. I'm surprised you didn't. How about a proportiing valve while you are at it.