I had a Howa 1500 in 300 Win Mag that shot and performed like a champ. Traded it off because it kicked too hard and was too loud. I now have one in 30-06 which is very good. You won't go wrong with either action, Remington or Howa.
Personally I'd go with the 257 WSM over the 257 WBY becuase I don't like belted cases. The Short magnums appear to be all the rage and if anything, forming brass for the .257 short mag would be a breeze. Even if the round is never commercialized, you could simply buy .270 WSM cases and neck them down to .257 in your sizing die. Weatherby brass is very scarce and very expensive. Also, he used that screwy radius shoulder and you have to fire form and jump through all sorts of hoops.
Just my .02 worth.
Do keep us posted on how your project is progressing. Best.