Off the top of my head, basically you will need everything that doesn't power the lights. This means the stator needs to be hooked up, the coils, the battery (cb750s don't run without a battery they don;t break even charging until 2K rpm), the regulator the rectifier, etc.
If the harness is already installed in the bike usually you can make a set of jumper wires to connect the wires from the engine to the corresponding ones on the chassis. I use 4 inline spark testers ($10 a piece at your aut parts store) to extend the plug wires to reach the motor, but you can probably just make some extensions out of old plug wire.
Cycle exchange sells a more modern reg/rectifier that is one piece and compact, if you are planing on using this you can build a temp harness around it using a battery and some spare coils. Then when it comes time to put it in the frame switch out your old reg/rect for the new unit.
