Scrape away the verdigris (green stuff) and see what the color is. If it's gold, you're good. If it's reddish or salmon colored, your bronze is de-zincafying and will become brittle and easier to break. Scrape away a lot, it can be good gold color in some spots and salmon or pinkish in other places.
Take a look at the Groco website and look for IBVF flanges. Traditionally there has been a mismatch between thru hulls and seacocks; tapered and straight pipe threads. Groco makes a three part system. A thru hull; a flange adapter that screws onto the thru hull and provides a big flange base for support; a ball valve that screws onto the flange adapter. You then add a pipe to hose adapter to finish it off. I've done 3 so far and I like the feel of the flange base mating flush to the backing block on the hull.
Groco has illustrations and Maine Sail has pictures on his pbase website.
You have several choices on how to fasten to the backing block. MaineSail's are the best but I cheat and use lag screws into the backing block. Mine felt very solid even without the lag screws but the lag screws provide insurance that you won't unscrew the flange from the thru hull even a little bit.