I don't have the set either, so am writing based solely on the pics that I have seen.
The main problem I see with using the US Cav as Confederates is the carbine. I can't tell precisely which carbine this is suppossed to be, but it appears it is a breach loading weapon. The south did not have the facilities to manufacture the cartridges for these weapons, so while they did have them (mostly captured stock) they were not regularly used by CSA troops, either horse or foot. It might be possible to alter the carbines to more closely resemble muzzle loaders, or even sawed off shotguns, both of which were regularly used by the CSA. You could keep a couple of figures with breachloaders to represent CSA cav that had managed to procure a captured weapon and a supply of cartridges. The pistol also appears to be a later version, but it is doubtful that this would be noticeable.
The Indian scout wouldn't fit with normal CSA horse, but if you acquired enough you could represent Stand Watie's Cherokee cavalry.
hi,the A C W period is the one I collect the most,and for this war theatre, we have a real luck,as modellers:the fotos of that period.ther are a lot of them on the internet...
to make C S A infantry ,arty or cavalry,you may use boers figures,or from U S cavalry,or mix figures of general staffs,either north or south,,if you paint them right,they perfectly fit and make illusion;
for the weapons or equipments,I'm sure you can cut, transform,or convert easily thoses soldiers.
just a word more:whith many infantry sets of other war theatre, you can make A C W soldiers, it is really easy to find,particularly from troops weaing shakos, that you can cut as a tosseled cap,and it is only an exemple...