I'm sure that hooker can provide you the exact measurements for you car, the hole size and location vary on those headers depending on which year car make and which motor, low deck or high deck
My 1969 Dart has had both B and RB motors in it and both sets of the Hooker fenderwell headers, the 1 7/8 and the 2.0 inch set.
I've cut the holes in one of my old Dusters and a 1968 Cuda, my Dart had them cut when I got it.
I had to cut more of the fenderwells on my last BB Duster due to moving the motor back as far as possible for better traction but I don't have any pictures of that one now