7 1/4 to 8 3/4 Newb Questions

I got lucky today, I found an a body 8 3/4 rear from a 71 Dart pretty local to me at a fair price.

My cars a 67 Dart GT, was orignally a slant car that a previous owner swapped a 273 into. Everything else seems to be original. The 7 1/4 is humming and leaking and I want to swap it out.

I'm taking the whole rear from the 71. 355 SG, with the drums, lines, shock plates and u bolts. I know I will require the the later model brake lines.

The one thing I'm not sure on is driveshaft length. The rear is coming out of a roller with no driveshaft. Will I need to shorten my existing driveshaft or will it mount up to the a body 8 3/4? Any idea how much it needs to be shortened?

Is there anything else you guys can think of that I will need to make this a painless on the ground diy swap?