Bill the only suggestion I can make about your current aluminum transom bracket is putty up all of the holes and the expansion slot, glue it back together as best you can, and use it for a pattern to cast one out of aluminum, brass or ductile iron.
FWIW (about $0.035 Cdn) if it was me, I wouldn’t bother with the aluminum. Silicon bronze would be my choice.
Hope this helps.
Best,
PM T2
He's livin' in his own private Idaho..... I hope to go out quietly in my sleep, like my grand-dad did..... and not screaming, like the passengers in his car...