Brian,
If i understand your question, I may be able to help.
If it's an externally balanced 406, then you'll need a external balance flywheel. You'll know when, you pull the flexplate, if it has a weight welded to the crank side of the flexplate, it's externally balanced.
If the flexplate doesn't have the weight, it's internally balanced, you can run a flywheel for a 350 etc.
Don't run the wrong flywheel though, ask me how I know.
BTW, Glad you're back. Hope this helps.
Earl,