I have a black rain billet matches set and I was interested in 458. Wilson do at has a barrel, BCG, gas block and tube for a good price. Looks like wicked ballistics in a standard ar receiver and standard mags.

With that billet set, you will need to open up the ejection port to accommodate the fat case.  I am in the middle of building a SBR in .458S for a pig hunt.  My plan is to send 500gr bullets at 1,050 fps out of a 10.5" Tromix barrel and through a Vers 50 suppressor.  Handloading the rounds was a no-brainer as I can load them for under $1/rd whereas buying them is about $3/rd.  If you go down this path, the best advice I can give you is buy more brass than you think you'll need because the stuff isn't produced regularly.  I bought 500 pieces of Starline which I think is more than a lifetime's worth for subsonics but with a gas gun in the field, recovering 75% of the brass would be optimistic IMO.  I also plan to load the 300gr .458S TTSX which are designed to expand all the way down to 1,000 fps and open up to 0.8".  Most of the projectiles you find for this caliber were designed for .458 Weatherby or other powerful cartridges so the bullets won't expand/deform/fragment the way they would in .458S since they're moving slower.

Hmmm. Maybe I'll get a different set. I don't want to modify the existing one they're already Coates in digi camo.