I have yet to do a full set of rockers in a 64, but I'm pretty sure the rail has to come off to get any of the back ones out. I distinctly remember hearing on here that the fuel supply line can be reused (connection at the fuel rail) a couple of times before having issues. These guys that have done them can hopefully chime in and verify that.
I have however, lost count on the number of transmissions and engines I have pulled, so I use a regular old 18mm wrench on the bottom bolts of the balancer. It spins pretty easy and the wrench will follow the balancer up in an arc motion, then I just reposition again on a bottom bolt and continue.