Soft top installation question

[my427cobra]

Hi all. I have a rather difficult soft top installation measurement question and I think I.ve searched all the past threads without an answer. So here goes.

My car is an NAF 427 fiberglass body. It is supposedly, from what I have read, a fairly close representation (contours etc) of the original Cobras. But the body did not come with the ferrules installed for the soft top bows.

I have the Cobra Restorers top and bows, which when assembled, the ends of the bows where they would go into the ferrules measures 52" with little flex in the bows that would chage the dimension.

So I'm going to assume that the ferrules will be 52" apart. Can anyone confirm that measurement for me on a Superperformance or Shelby car?

Now the tough question: what is the dimension to be used to locate the ferrules fore and aft?

A dimension back from the bottom of the windshield frame in front of thr door?
(this would seem to be the best measurement as the leading edge of the soft top starts at the whindshield and hopefully this measurement would put the bows in the right place relative to the windshield)

A dimension back from the back edge of the door? (chancey as not all bodies and doors are the same).

Any help would be appreciated.

Thanks, Greg