An excellent source of info on this undescribed sp. and many, many more is Thomas Weidner's _South American Eartheaters_, published/distributed by Cichlid Press. Some of the names have changed but you can't beat his first-hand knowledge, cited sources, and natural history of the Geophagines. It is one of the best aquarium hobby books ever published.
On a more personal revelatory note - sexing these guys isn't easy. At a larger size (around 4") there should be a noticeable difference in finnage length. Males have longer, more pointed fins. This is by no means a certain method, however. They don't have to be very large or old to breed, as some just over 3" have gone through the act (but didn't pull it off). Just give them time and space (in keeping with G. brasiliensis they are open brooders - they'll do it anywhere clean) and wait for the magic.
Just a rebuttal about them being "red geo braziliensis" - I believe they are still undescribed, sharing characteristics of both G. brasilensis and G. obscurus.
Good luck with them, I know you'll find them fun and easy to keep!
J