OK, sorry for the questions, but I want to make sure I'm understanding you. So, is your 67 R/T an automatic transmission car with a 8-3/4" rear end? (looking from the back of the car, underneath, the center of the rear end doesn't have any bolts you can see or any type of "removable cover") Does that sound right?
When you say "getting out the differential", you mean removing the "center section", "chunk", "pumpkin" etc. on the 8-3/4" rear end which has 10 bolts on the front of the rear end, right?
If so, then besides unbolting the driveshaft from the rear end yoke ("butterfly connector"), you also need to remove the axles on both sides too, THEN the center section will just pull forward/out. Each axle is held in by 5 nuts & a collar (passenger side is adjustable for axle play side-to-side). You can just remove the drums & take those nuts off without removing the brakes (just rotate the axles...there's one big hole you can put a socket through).