I've got a 3/4 inch setup from groco that I'm going to install...
The throughull screws into the flange nicely... no isues there... nps to nps threads...
The issue I'm facing is that the ballvalve connection to the flange, and the hose-barb connection to the ballvalve don't seem to let me tighten down through all the threads... this is a bit odd, as it does seem that there are enough female threads on both... I've put them together as tight as possible with a couple of spanners... and at least on the hose fitting, there's still 3 threads left... I don't know if I'd be able to tighen it so much once installed on the boat! The force required is tremendous!
I would contact groco. I found them very helpfull.
When I installed mine it went very easy. I dont know what to add.
When I did mine I installed the flange adaptor to a backing plate then glassed it to the hull over the hole. Then cut the thru hull to fit then installed the valve. I found a great photo explanaton on line but cant remember the site. Its hard to search from this phone.
That derelict boat was another dream for somebody else, don't let it be your nightmare and a waste of your life.