And you ain't kidding about being tough to drill! I probably dulled the center drill I was using in the tailstock drill chuck last night! I reckon it's some sort of ceramic in the center underside.
James Kenobi 1138 has a tutorial somewhere. Let me look.
You can make them with a V cut into the ends too which would give you good purchase.The trick to drilling them out was to create a wood “clamp” to hold them so you don’t scratch or dent them in a vice on your drill press. The jig was a hole drilled into wood, with a slot cut to the edge of the wood. Some of the filler in the amp ops is very hard to drill.
I’m looking for a photo of James’ jig.