SWEET!!!
"I was wondering if a more-accurate pack would be turned down in the name of uniformity, or if that would be encouraged?" Not turned down and yes encouraged.
"Did I read correctly that you can use nice leather pouches OR canvas pouches (or pleather), but not a mix of both?" Either or, we don't encourage mixing.
CRL:
Ammo Pouches
For 501st approval:
German MP-40 style ammo pouches.
Pouches are black in color and made of canvas, leather or leather-like material.
There are a minimum of two pouches:One pouch on the left shoulder and one on the right hip.
Option:A third pouch worn on the opposite hip.