In United States v. Janati the 4th Circuit finds that when a conspiracy is alleged the government must be allowed to show evidence of all the alleged overt acts, even if there are 1,300 and they were not specifically alleged in the indictment.
It's not Blakely specific but it could be a shadow of things to come.
There are obvious differences, of course. The government isn't asking for a jury finding on all 1,300 overt acts, just the 61 it actually charges and the conspiracy. The Court also makes a great deal of the fact that this evidential piling on is necessary because the prosecution is trying to prove implied intent (because, I guess they think most thieves run around broadcasting their intent to the world).
Still, it doesn't seem all that difficult to take that next step and order judges to allow all sorts of "overt act" evidence in to be approved by the jury.