IN Reagan's case - Ford will not be there. Bush I should speak as he was Reagan's VP, not because he was President; and Dubya should speak because he is the sitting President.
Unless there is a precedence for all FORMER presidents speaking at State Funerals, then Clinton and Carter need to Shut the hell up.
It sounds like the Dems KNOW this will be dignified and moving, and will be contrasted to the Wellstone Rally. So they HAVE TO try and make this look Political and Partisan.
The speakers at Nixon's funeral were Kissinger, Dole, Pete Wilson (CA governor) and Clinton. (Thanks to Google and the Nixon Library site for supplementing my memories.)
Ford said on Larry King Live that he will be there.