<VV> dual master question

[hugh]

When we purchased my wife's 65 convertible we asked for a dual master to be installed.  They did not but went out and bought a dual master marked 67-69.  Is there a major difference between between that and what is indicated for a 65.  I notice that Clark's seels a 65 for a lot more then a 67 so one concludes there are big differences.  
They also failed to tell me that the lines for the rear brakes were clogged so non-functional so you might say that I had half of a dual master after all.
I put one on my rampy from Clarks and it works but is spongy.
Thanks
Hugh