Moreover, perhaps we should remake this sidematch in a GAF image. Make it for the military arms of the era 1903-1916, ie prior to the involvement of the US in WW1. Rifle based, uniforms of the era associated with the rifles. No "cowboy" rifles. Here is where the SMLEs, the 03s, the Mauser 98s can come out to play. Stripper clips, bloc clips, chargers allowed, period speed loaders for the wheelguns.
I very much like that general concept I can already envisage "mixing and matching" various firearms already in my 'arsenal' - i.e. Ross or SMLE rifle .... and an even wider range of suitable handguns: Mark V or VI Webley, Colt Government Model, Colt New Service, S&W Hand Ejector ......
However, I can see a bit of a problem with the General's thought that WWI-era uniforms would not be allowed ..... unless he was thinking solely in the US context. Keep in mind that, by the end of 1916, the British Empire and the other major combatants (France, Belgium, Russia, Germany and Austria) had already been hotly engaged in the Great War hostilities for almost 2 1/2 years! And for the most part, they entered into that conflict in mid-1914 with uniforms, arms and equipment introduced at various times in the preceding ten or fifteen years .....
For example, the basic service uniforms, equipment and weapons used by British and Empire forces
throughout WWI originated in the 1902-1908 time period, following the Boer War .....
In other words, care would be required in how any restrictions are formulated.
On the other hand, if the primary concern would be to avoid inclusion of items which are really "WWI-specific" - such as steel shrapnel helmets and respirators (gas masks) - I would certainly have no objection to that .... indeed, neither of those items of equipment were introduced for British Empire forces, at least, until 1916.