In addition to measuring original fork rake, take a measurement of the frame HTA and perhaps consider a replacement with a non-original rake to better optimize the fork trail measurement to suit your purpose. Plug the HTA and rake into fork trail calculator at;
http://yojimg.net/bike/web_tools/trailcalc.php

Large manufactures are notorious for using identically raked forks over all sizes/angles of thier frame rather than custom fitting the rake to the HTA to achieve a specific desired trail, sometimes produces less than optimal trail. Also take into account the fork A-C measurement and consider what change that may cause if you go to a shorter A-C fork, unicrown forks tend to have a rather large A-C. 20mm change of A-C will alter your frame angles by 1 degree.