Green Board - It gets it's power like a normal arcade game, via the JAMMA connector.
Red Board - It uses a computer-type power supply.
I have swapped a green with a red, and a red with a green. The key is the power supply. If you are using a green board, you must have power in the JAMMA connector. If you are using a red board in place of a green, you do not need to power the JAMMA.
If you are swapping a green in place of a red, you need to make sure your JAMMA connector has the power wires attached, and you must make sure they are connected to the correct leads on your power supply.
It's not a difficult swap at all, you just need to understand how each gets it's power.
As for the "Complete"....it's all in the board. A "complete" hard drive will work just fine on a "NON-Complete" board, it just won't have the extra courses. I have a COMPLETE hard drive on an "7-course" board....it only plays 7-courses. If I get a "complete" board....I won't need to change the hard drive.