i think there was an optional flag/pennant staff available for a '75 Nineteen. i think it was the front nav. light that had the option. you and me got the nav. light w/o the pole. most of the pics of Nineteens in the AristoCraft brochures from their web site have the nav. lights w/ the poles for the flag.
looks like ya got a good idea to me. should look real good. only comment i have to the negitive about it is. me personally, i sometimes sit with my legs hanging over the ft. of the bow right where yer gonna put the pole at. if you don't use this area to sit at. yer flag pole will look great right there. if yer gonna use a back plate for the bolts, be sure the window pocket don't come that far fwd, i can't remember how far forward the pocket goes. i do think there is space between the pocket and the deck though. i lost my cat on board one day and i found her on top of the window pocket, so there must be a small space between the pocket and the deck.