You're welcome.
It is unlikely that you could fit a 1" bulkhead in a hole that is drilled for a 3/4" bulkhead unless some weird size was drilled. That is just really unlikely. Since the tank is already drilled with a 3/4" bulkhead installed you may as well use it. One thing you
can do is make sure that thin-walled PVC was used rather than thick-walled (SCH40) PVC. Using thin-walled PVC will give you a slightly larger internal diameter of the pipe and therefore allow a slightly higher flow. Just take the pipe size into account when figuring out head loss. I wouldn't change the 3/4" loc-line. You won't find 1" loc-line because it is not made.