if your wby is out of the 60'2 and the 257 is late model there is a chance the inletting is different. I do not recall the differences as I have not dabbled with old wby's. a word of advice, if the gun is in reasonable shape, DO NOT ALTER IT. the simplest stock mod could affect the value in a huge way. if you need to trim a stock, get another one to trim. also be careful of limbsaver pads on big kickers and short eye relief scopes......you might get a surprise.
I actually have 2 older Weatherbys that I inherited from my dad. One is an older post-WWII model that Roy Weatherby used to build off old beefed up Mauser actions. It's probably 1950's vintage. I saw one in Cabelas Gun Library the other day for about $2,000.00. That one stays locked up, and I don't shoot it.
The other one (the one I am probably going to restock) is one he bought new in the late '60s, after Roy invented the Mark V action. It appears to be no different than the Mark Vs that Weatherby makes today.
I don't plan to alter it, since, as you said, it will affect the value. That's why I want to replace the stock with a synthetic and a good recoil pad and hunt with it. I'll put the walnut stock (it really is gorgeous) away for safekeeping, intact.