It took over a year to find the right hammer-head in secondhand tool shops but the right one eventually turned up, it was perhaps an ancient brick hammer with a chisel back but the cast steel is really good. I patiently ground it down a bit each day it so as to not disturb the temper then fitted a hardwood handle.
Having a long time to think about this I brought all the big wall functions together by permanently fixing the funkness device and copperhead punch which all neatly stores in the handle. I made a double lanyard to reduce the chance of dropping it. Not that I’m likely to climb anything other than hammer-less aid but it was an interesting design exercise.