I have found the simple solution to switch back and forth between internally balanced engines (Steel Crank LA273, LA318, LA340's, B383's/RB440's ,RB413's) to externally balanced engines (LA 360's, cast crank 340's, B400's).
Note:all LA 318's were internally balanced.
A true high performance/Race engine should be internally balanced.

FIND THE RIGHT FLEXPLATE FOR YOUR MOPAR!
https://www.summitracing.com/parts/bm...
https://www.summitracing.com/parts/bm...
https://www.summitracing.com/parts/bm...