1967 Dart Drivetrain swap.
What would you recomend for a rear end? I see someone recomended the Ford 8.8 but I'm not sure how I feel about using a ford rear end in my Dodge. But I'd keep that option open.
i'm going to assume you'll want to be big bolt pattern (5X4.5) because it would match the most available and popular front disc brake pattern.
it depends on your criteria. how do you plan to use the car (street, street/strip with big tires & a lot of power, lots of drag racing, autoX or road solo, cruiser), are disc brakes a must, gear ratio (is LSD a must), are you able to do the modifications to the axle if necessary or will you have to farm that out/pay for it, and the biggest one: budget
if you're starting from zero, putting a mopar axle under your car will be the most expensive, bar none.
an 8.25 from 73~76 a-body is a bolt in and has drum brakes, this is probably the most affordable. gears sets and sure grip units are widely available and there are some (very few) disc brake options.
an 8.75 from 65~72 a-body is a direct bolt in and about the most expensive path. tons of options for gears and disc brakes, as well as aftermarket support-- the axles will need to be changed to BBP. you can also utilize 8.75's from vans, trucks or larger cars by relocating the spring perches, narrowing the housing, and axles or getting new axles. or you can open up the catalog and press the easy button and order brand new one spec'd to your desire at a credit card melting 5K (dana 60's and 9" run about the same, fyi)
for discs and an LSD, the explorer 8.8 is the absolute cheapest game in town. it's strong enough for general use, parts availability out the wazoo, and you can still pick them up pretty reasonably. obviously some modifications are in order.
some rangers also have 8.8's that are near bolt in affairs, but you'll need to carefully consider wheel fitment. disc brakes can get a little spendy, but there's diy options. mustang's offer some options as well, but again, modifications will need to be made. the benefit is that they're available and cheap. the same goes for 9" units, but you get strength and virtually ulimited choices in aftermarket disc brakes and gears.
i'm sure there's other, more arcane swaps out there but these are the more known and popular ones.
basically it comes down to: how strong do you need it to be, how much money do you have and do you want disc brakes.