I think the #3's would be way to haevy and to much for 425 HP ?!

A bad thing ,,,NO not realy,,just not comon.

They are def. stronger then TRS up to i say in that case (boatweight) 1000 HP each.

Usually 750-850 in heavyer boats.

TRS good for 650-700 HP.
The best thing would be to put Bravo's on it ,,u would gain 10MPH or so and the boat would lighten up at least 400 pounds in the back.

How much would the 3's be worth if selling?

Depends,,what shape and so on,,,gimbal ok or need rebuilt driveshaft sleeved or not,,,ratio and other things.

I say if ok ,,,between 3-5 K each ?! with the gimbals .