I started putting a 358 win together on a 700SA. So far, I have the stock, the action, which has been trued and I'm ready to barrel. In the mean time I've been reading about the 35/284. How hard would it be to steer that route from where I'm at now and what issues could I run into?

not hard at all. get the barrel and finding a smith with the reamer may be the issue. I rebarreled numerous 700's into 284 win. and the associated wildcats. never ran into any feeding issues with any of them that I recall. got a left handed 700 here now that will be for sale when I find the dies.

I had a 700 in 25-284 that was a fine rifle. A short action Whelen would rock

Id have to look at the neck dimensions to be 100% sure, but I'm about 90% sure you could stay on course and complete your .358, and then, later on if you were a mind to, simply rechamber to 35/284 with no other changes. I imagine the rifle will have a much greater resale value as a .358 (which has a bit of a cult following) versus the wildcat.
But if you really think the 35/284 is for you by all means go for it from the get-go. I have not compared the case capacity between the 35/284 and 35 Whelen, but if they are close, by all means try Alliant Power Pro 2000-MR in your 35/284 when you're doing loads. In the Whelen, that powder is a game changer (2700' with a 250g, 2900' with a 225g, Speer and Sierra published data, respectively). Don't know if you can fit enough in the .284 case though.

Good luck either way,
Rex

Hardly any difference 35 W c.c 69.3 and 35/284 c.c of 68.8 so less than one grain diff. So good luck. Cheers NC

Be aware that the OAL of the 700 SA mag box may run you into some of the same issues as the .350RM. I can't recall which has the longer case, but both are a good bit longer than the .358. This may rule out some of the sleeker bullets like the Accubond and TTSX. If you do go with the 284 case, a short magnum follower may likely feed better than a 308-based follower. It does on my 25-284 in a 700.

With today's good powders, I'd go .358win, but that's just me.

I'd agree with JPro and the others advocating for the 358 Win. But I'm no longer a fan of wildcats after having many. I think the only ones I have remaining are a 25-204 and a 250AI (not much of a wildcat....just improved).

I came close to doing a 35-284 a couple times but never quite got there. Had a Savage 99C in .308 I was going to rebore and I found two .284 mags for it. I think you can rent the reamer or use a standard .284 reamer with large pilot and then a 35 neck/throater. The mag length on a short action is a problem that would limit performance with anything heavy or sleek. I've still got a .35 cal Shilen blank waiting for me to get off my a$$ and do it, but it may end up being a .358 which I already have dies for or 35 Whelen which is easy too.