putting a ford 5.0 in a 72 Dart

Not to be rude, but that's a money-pit idea.
After the engine and trans are in and running and tuned, the rearend will need to go, new tires and wheels, upgraded suspension/steering/ and brakes. Then there's frame connectors, a 4-Link, and CalTracs. Then there is the hiway rpm, the hiway wind and body noises, and NVH (Noise/vibration/and harshness.)
Two years later, you got a 50Plus yo Dart-shaped Mustang, that nobody will ride-along with you in, cuz it rides like a truck..... and the worst of it is, you could have actually bought the Mustang for less, which will always have resale value, whereas the FrankenDarStang is yours forever..... lol
Jus saying.