Changing from 7 1/4" to 8 3/4" rear end questions

shove yolk in all the way. slide it out 3/4". measure from center of hole on slide yolk to center of hole on pinion yolk. car must be on wheels with full weight. take measurement to driveline place. done. if your re using current...take that too.
I don't have the motor/ transmission in the car yet. I was hoping to get all the parts gathered up to make the swap when I put the motor in. If I have to wait I will. Thank you.