What would be involved in rechambering my 458WM for 458 Lott?

Cost?

Pros?

Cons?

Who / where could I have it done?

The rifle is a Remington KS Safari.

Thanks for the help.

Your idea will most likely be decided by your magazine box and bolt length. If the mag box and bolt are long enough, it's an easy conversion. Based only on my memory, the Rem Safari was/is chambered for full length H & H based cartridges. If I'm correct, a simple rechamber w/ a Lott reamer is all that's needed.
Any competent GS can do it w/ a Lott reamer.
If you really want to "upgrade", then have it rebarreled to the Lott and new & better sights installed.

Thanks.