To do this cam adjustment is required and moving the timing belt one tooth forward or back is a rough and perhaps engine crunching solution.
So here the work so far.....
Stock Cam Pulley

Hub machined out

Vernier adjuster mechanism

Finished adjustable pulley - Front

Finished adjustable pulley - Rear

Will fit it this weekend and put it on the dyno to see how much effect it produces.
The middle ring of bolt holes progressively advances the cam timing depending on which hole is lined up and bolted as there is an incrementally increasing offset between each hole.
The inside slots allow for rotation and hold it all together when done, whilst the outside hold the hub to the pulley.
Will post the results - or perhaps lack of, after some testing.