* Only three of six venues ready for Confederations Cup * FIFA acknowledges stadiums will not be fully operational * Brazil expected to deliver usable but unfinished venues By Anthony Boadle and Andrew Downie BRASILIA/SAO PAULO, April 10 (Reuters) - More than half a million tickets have been sold for the Confederations Cup in June, but host nation Brazil has yet to finish the main stadiums to be used in the dress rehearsal for the 2014 soccer World Cup. On the eve of yet another FIFA deadline, Brazil has delivered only three of the six venues for the eight-nation warm-up starting in two ... More...