I can't spin the output shaft by hand. Even when I had it out on the ground, it's incredibly hard to rotate without something on the shaft to give it more torqueYes. You want the gap to be as close to even as you can get it all the way around.
Yes it will. I have a Blue Truck out in my driveway right with a ZF5 and the T-19 plate. I pull the very top part (shifter tower?) off of the transmission and put rags, paper towels, etc inside the hole to keep the crud out during the install. It's a tight fit, but it will go. This is also the reason why I can't s c r e w my shifter boot down to the plate. The shifter sits too far back for the holes to line up.
Now, back to the problem at hand. Do you have the transmission in gear? If not, put it in gear. Then spin the output shaft of the transmission. Spinning the crank bolt will do NOTHING to align the splines if they're not aligned. Why? Because the pressure from the input shaft of the transmission keeps enough pressure on the clutch splines so that the input shaft will spin with the crank/flywheel/clutch because there's nothing to keep it from spinning. That only works when the driveshaft(s) is in place. By putting the transmission in gear and spinning the output shaft, you are spinni9ng all of the internals of the transmission but not the clutch/flywheel. That's how you align the splines when you're installing the transmission.