robert
granted, it,s a bit unorthodox, but i can,t see how tophats can be safely used when there,s only about 1mm of valvestem protruding fwn.
here,s a ground down shim from the piper inlet (the autosprint cam has stock size shims), it just burnishes a contact point and shows no signs of wear (just checked my mot, done 26k miles since april 
)
http://www.micra.org.uk/attachment.php?attachmentid=11338&stc=1&d=1230213441
http://www.micra.org.uk/attachment.php?attachmentid=11339&stc=1&d=1230213441
