Thanks all for the responses. It' turns out, no pun intended, that I had >6 but <8 full turns before I reached tightness. I am confident that I have enough NPS thread into the flange to insure a good seal and one that won't easily unthread. Before I threaded it in, I cleaned the hole well with lots of OMS and Acetone, allowed to dry and then coated the inside of the hole with a layer of 291. Then I gooped up the threads of the thru-hull, threaded it in and really snugged it down.
Next week, when I get splashed, will be the test.
If you liked my advice/response, give me some rep points. If you didn't......well what do you expect, it was free.