The OD engages by oil pressure so you'd need to rotate the GB input shaft at about 1500rpm to emulate car conditions. Solenoid switches the oil circuit so that it provides the pressure when needed. You can check the solenoid electrically but otherwise it's down to fit and test. If you can road test the care, carefully, after it's fitted and before you weld up the new tunnel, it'll be quicker to get it in and out. Remind us of what you are doing as unless you're going remote change you shouldn't have to mod the floor.