Looking to possibly put a Dana in my Dart,few questions for those in the know.

First, I love your car Sanity!

If you are frugal in purchasing stuff, you can build a rear for under $1K. $1200 with a powerlock sure grip if you want to go that direction.

Rear $100
shorten $100
ends $80 Dr Diff
axles $300 Dr Diff
powerlock $150
gears $50-175
bearings $120 Dr Diff
set up $150

$1205 buy my count using the high side price on gears

Use the brakes from your 8.75 rear

It's all a time/money thing. Take longer to build them, more convenient to make a call to the Doc.