Re: bronze or stainless portlights?
Ours are bronze. 85 years old and still like new.
In the short term the stainless will be fine. In the long term, the bronze will do better. If you must have shiny-all-the-time bronze, then it's back to the stainless. If you like brown/green patina, then it's over to the bronze. If they're gunmetal (a form of bronze) they will age w/o turning so green and they'll be a bit more brown than green.
Which shape are your old ones? Are you doing an exact replacement or making it slightly different?
"The only noble thing a man can do with money is to build a schooner." Robert Louis Stevenson