I found this nugget while reading that thread -
"Ken Howell's book Custom Cartridges lists it as the .444 Marlin Rimless (aka .425 Rimless Express.) Basically, a .30-06 basic case trimmed to 2.225" (same length as the .444) Headspaces on the mouth just like a .30 Carbine."
Interesting, no? That would eliminate a great deal of effort. ".30-06 basic" brass. I wonder if that means untapered. I know the "45 basic" brass is what .45-70 is made from, it is trimmed down to size to make .45-70. Where to find "basic" brass is the question.
"The 10.75x57 Mannlicher was chambered in both the 1888 and the 1898 Mausers.
The 10.75x57 was the 8x57 expanded to .424 bullet diameter,it was introduced around 1900 and became obsolete within a few years.Measurements were base .468,shoulder .465,and the neck was .448.
It is believed that headspacing problems were responsible for it's being dropped from Mauser's line of chamberings.Feeding problems and the fact that it was underpowered for the game it was used on may have contributed to it becoming obsolete."
That's another option - use 8mm brass. The 8mm base is very close to a .308/.06 base and in some cases (if not all) the bolts are interchangeable. A neck of .445 should work for for a .45 build as well... slight reaming and it would be perfect.