for the screw holes use a wooded dowle soaked in resin, hamer in and cut iff when dry.
I would fill both holes as when you have the bracket on it will
one, seal the bracket for floation,
Two is you ever get a leak from the bracket it will fill the boat in no time!
To fix the holes I would glass from the inside of the boat to cover the hole, then you can cut ply, coat with resin and cloth and fill from the outside.
Then run the wires and stuff thur a new transom hole and vac hose, like this:
