A new front end is in construction and as a result a new spacer set for the front end is required. The forks will be original to the 1991 XJ600 this time so the calipers can be used on the current front wheel. In fact all the parts can be reused except the speedo sensor (which is not present in the new front end). So a replacement spacer that fills the gap of the speed sensor is needed.

Dimensional drawings and basic illustration below: