From what I understand, swapping a 20v into an ST also involves swapping the wiring harness.

I've never worked with stand alone, so I have a dumb question here:

Could a standalone be used to operate a 20v while leaving the stock 7A wiring harness in place?

Why or why not? As detailed an explanation as possible would not be in vain, as I promise Ill soak it all up. =)

The stock 7A plugs don't fit the 20V 4A-GE. Also, some plugs are missing, such as the VVT plug and such. If you go standalone, I'd create a custom harness or use the 20V's harness.