rembo-
In American Hunter of Feb 1985, Finn Aagaard listed two loads as being .45-70 equivalents, one using a 300 gr bullet and the other a 400 gr bullet.

In Handloader May-June 1978, Clay Harvey has an article titled "De-Magnumizing the .458 Winchester Magnum" and lists several loads with 300, 350, 400, and 405 gr bullet.

Several light loads in "Reader By-Lines" are listed in Handloader 81 (Sept-Oct 1979), page 10.

Ken Water's Pet Loads article on the .458 in [Handloader[/i] 92 (July-Aug 1981) lists several reduced loads with 300 and 400 gr bullets.

The starting loads listed in the Lyman reloading manuals are about the equivalent of .45-70 loads. I think the Speer manual also lists reduced .458 loads.

Ed Matunas wrote an article in the 1990 Handloader's Digest titled "Handloading the Really Big Bores for Deer", and listed some .45-70 equivalent loads. Ray Ordorica did the same in the 1994 Handloader's Digest titled "The 458 Revisited".

Just some places to start looking.
--Bob