I have now done some fine measurements. The UFM where F28/1 mounts was 5 thou out of alignment. The shaft on the IKON was nearly 20 thou out of true! And so a simple job gets more complex. The UFM was straightened with moderate brute force and now a Koni is a good fit. The Ikon will be sent back to the factory for rebuilding. At no stage would I have considered fitting what Vic suggested until I had explored all avenues. I will fit spacers either side of the shock to keep it centralised and prevent any side torque.