Driveshaft length 8 3/4

Hi Folks,

I own a 1964 Dodge Dart, put in a 318, 904 automatic (not pushbutton type) and it has a 7 1/4 rear. I am going to an 8 3/4 rear axle, 3:55 suregrip.

Does anyone know what length the driveshaft should be for this combination and exactly from what two points the measurement is taken?

Thanks in advance,
Mark