I will try to answer better, when I have more time but the thread may disappear from the first page by then.
I agree with cavcrazy. I have the Tiger's.
Crook had a better pack train than Custer. I believe he used all aparejos packs. A literal translation is commonly rigging. It did not use the sawbuck.
Here is a link to an aparejos site. It has illustrations. Of course the load will vary. But both ammunition and hardtack came in wooden boxes.
link
Here is link to a photo of a sawbuck saddle:
link
The aparejos was much superior. It was easier on the mule. I think it may have held the load better as well. However, sawbucks are still commonly used today. But they are not used for long military campaigns.
I doubt if there would be much visible difference for a 28mm model once you had the load on.
I have a photo of one of Crook's mules at the end of the 1876 summer campaign when they had obtained flour in barrels from the merchants in the Black Hills. The photo is in a book. I would have to try to photograph it and post it here. That may take me a few days.
I also have an article by John Gray on Custer's pack train that may refresh my memory more. But I think Custer had his ammo, maybe not all of it, on aparejos saddles and all else on sawbucks.
Actually for game purposes, cavcrazy's suggestion is probably the best you are going to do. I never saw any others that were that appropriate. With hardtack and ammo both being in boxes, the Tiger is probably the best bet.
Tom