Balance factors: 383 steel crank vs. 400 cast crank.
They both use the same rod.
They both use a piston that's the same or very close weight.
383 cast cranks used exactly the same factory imbalance as the 383 or 400 cast cranks. And they were somewhat interchangeable on the assembly line, between cast and forged 383s.

My opinion is if you remove the 400 cast crank and swap in a 383 forged crank with the 383 harmonic damper and flywheel/torque converter, you will have a typical Mopar factory balance job on the result.
The Mopar balance jobs aren't known for their precision, but we didn't hear about any problems back in the day. Now that everyone is balancing to a gram or less, ANY Mopar factory balance job can be improved. But don't expect a noticeable difference.
So swap away!

And, if you're hoping for 10:1 compression without changing pistons, dream on...you'll never get there.

R.