Bob,
This one is very basic and works on the principle you mentioned. Make up a larger cam shaped blank, ali or even plywood (say 4X scale) and use that to control the grinding head.
I have seen many, and I think I have other plans somewhere, of very complicated machines for grinding cams. But I don't think any of them come close to this for ease of use and construction.
The big boys who make the blown V-8 models use this one.
If you can use a mill or lathe with a bit of confidence, no-one should have any trouble making and using this.
I suppose, at a push this one could be used for making full sized, just make it a lot wider.
John