use lots of pb blast and for the rear mani rock the motor forward, other than that just work them around till they come out same for installing the new ones. I usualy just get pissed and break stuff like my back valve cover trying to put slp headers in.
Let the old manifolds soak overnight in PB blast, and make sure the engine is very cool. You may break some bolts, so be prepared with backups. Finally, have a bunch of different kinds of sockets, all 13 mm i believe, but you need deep socket and regular.