7 1/4" to 8 3/4" rear end swap advice

What he said. The dolly doesn't help you lift it, so is pointless.

Just make sure the rear has the same u-joint size as the driveshaft. You might need an adapter u-joint. And you can have a driveline shop cut down your driveshaft to length, if necessary.

Does your Dart have disc brakes? Because the 8-3/4 will have the 10 x 1.75 drums — that makes a bad combo with the base 9" front drums, though it's OK with the 10".

It's possible you might need a different e-brake cable. You'll just have to see if it works out.