Changing the rear quarters on my Dart conv. from a 69 to a 70

I have a 69 convertible that I want to make into a 1970. Changing the front group is easy but doing the rear quarters will be a bit of a challenge. If anyone has done this and can post any pictures taken during the process so I can get any ideas on how to tackle the problem of where to splice the quarters, that would be helpful on how to proceed. I have everything from the rear of a 1970 that I had parted many years ago.
You should know better than anyone here, being you have both parts on hand and can measure yourself. I had both cars myself a few years ago and I think the 70' may be a little shorter on the frame rails. I would say let the frame rails tell you where to cut, but keep in mind that you will need the side lights in your cut from the 70'. There will be a lot of changes in the front also, hood fenders grill and power to the side lights, front and rear. Hope you saved your rear wiring for the tail and brake lights from the 70'.