Your Thoughts
I am, for some reason, very much wanting to build a hunting rifle in 284Win.
Reasons I think you should re-think your thoughts.
There is nothing a .284 can do better than a wsm can do. You can load the wsm down to velocity of a .284 or you can step it up to the 7mm rem mag and 300wsm and more find ammo anywhere.
Brass is very hard to find for .284 ( you could neck up 6.5/284 Lapua some work required)
There is little reloading data for .284 what there is not up to what a bolt action can handle, Winchester loaded very moderatly as there Win 88 & Model 100 where not strong like a boltgun.
I would think resale value of a .284 would be much lower than the wsm (no Loaded ammo available)
I built a & 7mmwsm Rem trued action short, Hart 24" barrel, McMillan stock it was a shooter was driving 140gr Noslers at 3290 fps and very accurate, but it kicked hard gun with scope weighed 7lbs,it had a Rem magazine and cycled rounds well.a member here bought it and loves it and has shot lots of game in BC.
But the 7mmwsm is dieing as well hardly no manufactures offering it any more.
the American & Canadians where brain washed by the late Jack Oconnor on his 270win.
I read where he said the .280 rem was a better cartridge.
Just my thought
Manitou
I agree with some of what Manitou has to say. The rarity of the .284Win, for brass etc, can be hard.
As for load data,....well there is much established load data, even if it was to shoot reliably in 88's and 100's. Every rifle is a law unto itself remember, so you have lot's of starting loads for a strong bolt gun.
The 7mm/08 is right there in lighter bullet's, but it will not match the .284's capacity on the heaviest bullet's. You did say you are going 26", so that will wring out the case capacity. 7mm/08 is great,...but in a custom,...it's like telling you to use my favorite .308, and not build a .284. Customs are just that, put it together the way you want it,..not for me remember, but nonetheless give here a shot.
The .284 was the first WSM, long before .270s and 7mms arrived on the scene, saying look at me, I'm new,.....and trying to push established go to cartridges like .270Wins and 7mmRMag's around.

I owned two, .284's over the years, and really like the look of the cartridge. Didn't reload, they were both 100's. Will it feed? Will a WSM feed? This will probably answer your question.
Usually I'm the one who tries to talk practical like,..." Buy a .308, buy a .270Win, or a 7mmRem Mag,..get a BLR etc etc.........but seeing as I've felt a few jabs thrown in on a couple of my pets(.270Win/.284Win), and I don't care much for WSM's


,...... I'll tell you what I'll do,...
.......you build your custom .284Winchester(World's first and most revered Short Magnum),...........post the pic's here for me to see,.... and I'll ship you at no charge to you, enough once fired brass, to keep you going for a few years anyhow.