Originally Posted by
Cassave
One option, take the fork to a shop and have the crown race seat milled to 26.4
+1 this. May as well get the head tube done at the same time (JIS = 30.0mm Ɵ; ISO = 30.2mm Ɵ)
or compare the crown race on both the headsets you have, it's likely that the 27.0 will work with the purple headset.
First check that your old crown race isn't worn; that part is
always the first part to wear out on headsets.