Barney-style 83/4 build

So I will soon be building an 83/4 for my 70 Dart. I got an abody rear but it's still got the sbp axels and I have no clue what the diff is, other than being 90% sure it's an open unit.

For now the diff will be left alone, I bought this rear from a member about 1.5 years ago who told me it just needed some oil and it's ready to roll.

Where do I get axles for lbp? What else am I goin to need for the build? What would be your best guess at the gear ratio of a 71 abody 83/4? What u joints and other misc things do I need?

Side question, I'm swapping up from a /6 to a 360 with RMS Suspension. Is it better to shorten a driveshaft or just get a new one?
Thanks!