Having taken the advice of my betters and read some books, I made a determined effort to get this to work, so perhaps a bit OTT but...
I took a short length of cast iron bar (ex casement weight) and drilled out the middle to make a small pot. Then I ground up the Eternite to a fine powder put the Eternite into the pot added in the tappets and cams tamping down the Eternite between components, topped off with Eternite popped on a little cast iron lid then warmed the whole lot upto big propane torch temperature in an insulating cave made from old (modern) gas fire insulation and kept it orange hot for 15 minutes and then left to cool for 30 minutes.
Then I quenched the pot retrieved the components, heated them back up and quenched. Now the file won't touch it. Everything looks nice and evenly baked and is polishing up well.
Apart from a charred workbench - the insulation wasn't quite as good as I thought...