Make sure you are using Wooden Wedges, a bunch of them all around, in the gaps between the block and the head!
Use six or eight of them.
Whack one with a hammer, then move to the next.
I did it in the past and it will work, if slowly.
Move from whacking one wedge to the next and back again.
I trust that will work and the wood will keep the block and head from being damaged.