Jimbo.... How can this job be so difficult? It just needs a nicely fitting valve spring compressor, capable of doing just that, compressing the spring. Yes, with age, heat, etc the collets can stick, so the trick is to set the tool with just a little bit of load on the valve cap and give the fork end of the tool a little smack, as mentioned. This shock will break the adhesive grip between valve cap and collets and the cap will only move a small safe distance, down the valve. No drama, easy. Now winding on the tool will move the valve cap and spring down the valve stem, exposing the collets which can then be extracted.
When reassembling, I smear the collets with grease, which holds them in place on the valve stem and also helps the valve cap settle back into place.
In the old days, Sykes-Pickavent were the popular brand, these days the world is your lobster.
Chaterlea John's is a clever trick, but not for the feint hearted. Also finding a flying collet in among the rest of the stuff turns a simple job into a nightmare, and like magneto armatures, valves don't like big hammers.
RD...I did a similar mod for Ford CVH type engines, allowing use of my usual Sykes tool.
Swarfy.