Thanks everyone - found the root of the problem I think
I stripped the piston from the undamaged conrod - the top conrod oil feed hole is not in line with the hole in the bush - it looks like it has turned, but not sure why?
Would it be fair to assume the same had happened on the broken side, causing the bush to fail? etc, etc
When I bought the new NOS conrods, the seller immediately said it sounded like it had not been line reamed and that was the cause
Opinions welcomed
Cheers
Charles