Brian,
Just to touch on a point you made about the 2.8" case of the 458 Lott re 2.85" case of the 375H&H. When you blow out a 375H&H case (in the Lott chamber) it shortens a little. I gather basic magnum brass was hard to come by back then, and Jack simply used blown out 375H&H cases.
CptnCurl: I had a CZ550 rechambered from 458WM to Lott. My 'smith didn't use a Lott reamer but rather a "458 throat cutter" and pushed it in furthur. Can't remember the details as it was over 3 years ago, but ask your 'smith, they'll probably understand. No modifications were required to get the rounds to feed, but modifications were needed to get reloads with 510gr Winchester softs to feed reliably. If you plan on going to Africa with your Lott, then it may benefit to have your chamber cut to take a Lott with 2.85" case as that's what's become factory available in Sth Africa (I believe?!). Personally, that should be called a 458 Watts, not a Lott. Regarding shooting 458WM in the Lott, I'm gearing up for a big range session in the next few weeks with both my Lott and WM, I'll make that one of my experiments and get back.
Soon my Lott and WM will be joined by a Capstick... passionate about Big Bores.... you bet! If you ever hear of some Australian carrying a 30M1 chambered bolt action for rabbits and whistled foxes, that'll probably be me!
Cheers all...
Con