Choices:
4+ inch stroked 360
440
511 stroked 440

Any of the above will do 500 hp easily using modern parts.

Stock Mopar engines of that era were hampered by three design deficiencies: 1. Cylinder head flow 2. Compression 3. Huge (heavy) reciprocating parts

So for any Mopar engine of the ages in question, plan to replace cylinder heads with your choice modern aluminum head, work with us to get the compression right, and also in choices of rotating and reciprocating parts.

A good place to start looking are the online vendors, starting with
www.440Source.com
Campbell Enterprises.com
Mancini Racing.com
Todd Marsh of Marsh Performance

If you look into the Moparts sponsor lists you will find many good guys who live in the Mopar world. There are many tricks and traps to building a Mopar engine from the ground up.

If you stick around here long enough you will begin to understand that there are board members who think a car is driveable if it idles at 1800rpm and gets 4.8 miles per gallon of race gas. SO, take cam recommendations with a grain of salt.
There are a thousand ways to do ignition but there is no need to spend a zillion dollars unless it satisfies one of your urges.

Sometimes you will ask a question and there will be a tornado of contradictory opinions. Don't be afraid to send a PM or two to get rid of the chatter.

Don't start buying things before you know which way you're going.

Don't jump at a particularly great deal on a particular part and then have to stand on your head to build the rest of the engine around it.

Realize that by increasing the engine power in your car by 150 lb-ft of torque or 125hp that you will need to redo many of the systems such as drivetrain, brakes, chassis, etc.

Finally, DO MAKE A BUDGET and be truthful about how much you are willing to spend.

R.

PS: I speak from experience on these warnings. My first cam swap resulted in the engine power increasing enough that it overpowered the suspension and I wrecked the car.
I have a mountain of really excellent parts that won't fit my current needs, but they were a great deal at the time.
I have another mountain of parts that have become obsolete before they were ever used. This represents literally thousands of dollars that have been spent with no chance of getting them back, or putting the investment to use.
So if I can help you avoid those pitfalls, it would make me feel better about my own mess-ups.