A .45/70 case has a rim over .6" so should work for a gaurd in .54's just fine.
I neck cases up using a variety of expander buttons I either make or buy. A .44 neck expander willneckup standard brass, ie: .468" head, like 8mm, .30/06, whatever - about straight. This will add another 8 or so to the capacity.
Second row from the bottom - 5th case form the left is a .458 Alaskan (my own wildcat) necked up to 50 cal, virtually straight before turning the end round. The 9th case from the left,in about the middle, same row is a necked out .30/06 using a .40" expander die and has 70gr. capacity. The 3rd case fromt he right, same row, has had 1/2 the neck removed from an almost straightened 8mm mauser case for 55gr. capacity.
Second row down from the top, counting right to left, I used .300 WSM brass, with the necks and shoudlers turned off. They run 58gr. to 66gr. depending on the length. Powder measrues -1,2,3,4,6,9,10 & 15.
The bottom row are .223 cases shortened to hold from 15gr. to 25gr., with the one on the far right holding 30gr. and made from brass tubing.
The first ones I made from cases, years ago, I didn't bother with the rims or extractor grooves, but I feel they look much better if those are turned off.
An electric drill held in a vice makes a poor-man's lathe and is the method I used for all turning brass and steel, using files, prior to getting my Dad's little lathe. It's interesting on how 'fine' the work can be and what can be accomplished once you can get some practise.
The 2 on the far right, top row hold 125gr. and 140gr., both made from the hobby shop .015" wall tubing with pine plugs in the ends.
I'd much rather have a fixed measure, than an adjustable one. The adjustable measures (yes I have several), made of brass are OK, but heavy, clunky and anything BUT period correct. I also prefer brass tubing to horn or bone as it's more accurate. The larger the hole in the top end of a measure, the more variation in powder charges you throw each shot.