Simon, thank you, the washer sounds a good idea and I was mulling over about grounding the cavity tape.
My thoughts are to earth them all to one point to avoid earth loops.
The pillar drill at work did not have a big enough throat to accommodate the body so could not use that.
I spent an age measuring either side so that I could drill in from each side to hopefully meet in the middle.
The string ferrules I bought are an 'all in one' type so I carved a trough in the back rather than six individual holes.
Don't think I would fancy drilling six individual holes without very sharp bits and a pillar drill but
others more skilled than me may well have done it successfully.
Having done the ferrule thingy it is back to glossing the body.
Onwards and upwards !