Somewhere I had a tiny photo of a C-clamp in place with spacers to clear the ends of the rocker arm pivot shaft, but cannot seem to find it now.
Duane Asherman's site (also a good generally resource) has some good info and picture of someone doing this process with a gigantic pair
of Channel lock pliers, but that isn't my preferred approach, and it kinda requires 3 hands and holding one's mouth just right to do it that way
with success...