I've been looking to game the Great Paraguayan War AKA: the War of the Triple Alliance and I think 6mm would be perfect, though I've never collected 6mm armies before.

Has anyone doen this using the Baccus Rane? I'm sure the ACW range suitably painted would proxy quite well along with some Pony Wars figures as well maybe? Is there anything that could be used to represent the Paraguayan Infantry Chiripa/Kilt?

Could some of the Napoleonic French maybe be used for the Argentines?

Would the Polemos ACW rules work for this? 

I've done it in 6mm with proxy armies (mix of Baccus and others): ACW for the allies, British/East India Company for the Paraguayan infantry, assorted Crimean Russian or 1877 Romanian hussars in red for the Paraguayan cavalry. You can get away with a lot in 6mm! Flickr album here; game reports here and here.

ACW inf in long frock coats might work for Paraguayan kilts.

Thanks Chris, that's very useful. Without too much Bias (or a lot), how well did the BBB rules work?

Glad that helped. For unbiased assessment of BBB in general, check out the Collected Reviews page here.

As for my very subjective view of how BBB works for the Great Paraguayan War: I reckon its menu of different Attributes for different troop types does a good job of bringing out the different flavours of the different armies and capturing the asymmetric nature of the war. Particular exotic events or circumstances can always be catered for by scenario rules.

Alternatively, you might check out the Borders of Blood rules written specifically for this war: Borders of Blood: Wargaming the Paraguayan War 1864 -1870 | Board Game | BoardGameGeek (NB I haven't tried them so this is not an endorsement, just a different option if adapting more generic C19 rules doesn't give the effect you want.)