If your drive has the internal True Course steering be sure to turn the steering wheel both ways and split the difference. Square the upper, I always measured from the rear of the trunion ears to the front of the exhaust housing. Be sure to disconnect the battery, you do not want to melt the stainless shift wire when you are busy shoving it through.
If the stainless cover that goes below the pump housing has a machined taper that is where the “O” ring should go. But do not lose any sleep over it if not. That is why I always sealed it and the bolts with #2 Permatex.