Your example is almost like John's example. The only difference is in the width of the fabric he uses in the example and yours. His is 44" and yours is 43.
If you will just substitute your figures for his in the the example you will see what the additional measurements are.
I do note that he adds 3" to the width of the quilt and 6" to the length.
However, I did the forumla and get that you need 82" of fabric to do the diagonal method.
The forumulae is 66 + 66x(51-43) or
____________
2 x 43-51 or
86-51 or 35
So 66 x8
_____
35 or 15.8 inches and 66 + 15.8 = 81.08 and I would round it up to 82"
I find that I must go back to his formular illustration and plug in my measurements before I can do it. (everytime) sure better than buying two length of the fabric.