I have a Model 70 Winchester Custom in .458 Win Mag. If I have the chamber reamed to .458 Lott to I have to do anything else to the gun to make it function, load, shoot, or whatever to do it right? Thanks, all help appreciated. Mike

The receiver will have to be milled to take a H&H length magazine box and the stock re-inletted for it. Feeding might still be a problem, depending on what bullets you use and seated to what length. You'll also need a magnum follower.

My M70 (classic '06) has a 3.8" ejection port, and a magazine with a filler which when removed brings the magazine length to 3.8" inside.
I've been considering the same thing, but different, and seems to me you'll need the .375-sized boltstop, mag follower and ejector (all available thru Brownells). This'll give you the bolt throw you need, no loss of capacity (3+1) and case head clearance for feeding.
Then, of course, rechamber/headspace.
It looks like M70's only come in "short" and "long," with or without spacers for medium-length cartridges.
There is no doubt JBelk knows more than I do about it, but this is what my gun measures. Doesn't seem cost-effective to produce the safari mag in two length actions for 458WM or 375/416.

My experience is with pre-64 M-70s. They could have changed something but the fact is that the Lott is on an H&H case and the 458 Win is a 2.5" case.

My advice would be to make sure the magazine is long enough before committing to a re-chamber job.

Thanks guys. I think I will leave it well enough alone since it is a custom job and I don't want to destroy the intregrity of it. Time to dig down in the sock again I guess. Mike