CZ 457 Varmint Arca Rail?

Edit: - my experience is irrelevant as it was done on MTR stock

If this helps, I put a 10” 419 rail on a manners eh1. Not flat or even remotely made for a full length arca. I drilled the holes where they needed to be and installed the T nuts from the inside all this like a typical installation. Then I taped off the stock and roughed up the stock surface under the rail. Waxed the bottom of the rail and put a skim coat of devcon under rail. Put rail on and installed screws without tightening beyond getting the rail in place so I didn’t bend the rail but let the devcon fill in the void. Basically no different then bedding a scope rail to action back in the day just with more devcon. Worked like a champ and ran two seasons of nrl hunter without anything loosening or problems. Hope this helps.

Salmon River Solutions makes arca rail that is curved.
They might have a solution. Get it? Ha ha

Not an ARCA rail, but I put an Area 419 picatinny rail- 5 inch- on my LH 457 varmint last week. The ARCA is wider isn't it? I haven't used one. Anyway the picatinny fit fine side to side but I had a small issue lengthwise. At least on my stock there is a slight outward bulge, so the rail will not touch the wood along its full length. I tightened it down such that there is about a one millimeter gap between the rail and the wood at both mounting holes and the rail is on the wood about the center three inches. Seems stable so far.