Some people feed cord in through the spark plug hole and use the piston to push up on the head.
This has always worked for me. I've got soft rope that I put through each spark plug hole. Then, a slow movement on the kicker breaks it free.
I usually do the same with the barrels... leave the nuts and bolts finger tight in the head, loosen the nuts on the base of the barrels, push down on the kicker and it's good to go.