Hi Jackie
I was told (though I don't know how accurate that is) that all those moved had been transferred to the new cemetery - though not all their gravestones were, as some were too wide. The newspaper accounts of the time don't mention any being moved to elsewhere in the Old Church, only those moved to the new cemetery.
if you visit the new cemetery there is an area which has nearly all the older stones (before 1964), and a few spaces with no gravestone, so I'd assumed that was probably also for people moved from the old churchyard but without a gravestone.
either way, we didn't see a stone for your grandfather, sorry.
best wishes
robbiesmum