I'm Cummins swapping a '74 Duster, thought I'd share the progress.

OK, @Daniel Garcia, here are my thoughts:
1. Go for it. It's your car. It's your plan. And I think it will be cool.
2. I saw where a V10 Viper engine was put in a Mopar (an E Body I think). I wonder if people told him it would never work out? I KNOW that stuffing a 6 cylinder diesel in an A Body is different, but the concept is the same. You are stuffing a bigger motor in your car than it was designed for. Go for it.
3. Will it be safe? I see no reason why it can't be. I assume you have no intention of just cutting and hacking until the big motor is in there. I know that you are going to strengthen and reinforce everything as you go. A heavier car will need better brakes, but I bet you already thought of that.
Overall, I would say this. Can it be done? Yes. It is a matter of how good you are at problem solving and fabrication. As long as you plan it out, take your time, do things properly with an eye on strength and safety, you should be good. I can't wait to see the finished product. Hey, I am only one state away. When it's done, can I come and get a ride?
Specifically regarding the brakes I'm planning on using some willwoods, backed up with the hydro boost system from a Ram truck, haven't figured out which set or size yet since there's a lot to consider with all of that and at the moment I'm mostly worried about getting the engine and transmission in the car, as well as doing the necessary stiffening and strengthening (which will be done as soon as I figure out where exactly everything is going to sit).

Ideally I would like to maintain the classic muscle car look with wheels and tires, y'know big meaty tires on a smaller rim, but I'll compromise on that in order to safety stop this freight train.

As far as the ride goes, by all means!