Ok, I didn't went throught everything, but in the link to build a 9000-RPM head, there is a link to Tomei English Manual that says "Nissan Motor Recommends clearance of: 0.14~0.17mm (when cold)". Here's the link to the PDF Document!
http://www-personal.umich.edu/~taesoo/SRHead/Tomei%20Manual/TomeiManualEnglish.pdf
I know this is for Tomei, but I'm pretty sure the Rocker to Cam Clearance should be the same for HKS
Also, I was about to ask the same question, so I guess it's a nice thing! haha
EDIT : Jspaeth, you are right about guides coming in only one size from nissan, but some companies make different ones!
Frank